Rick Kretschmer's License Plate Archives 

All-numeric serial formats, no stars or blank space along left side. 

Pneumatic tire motor vehicle (usually a passenger car) 1914-1917; passenger car regardless of tire type 1918-1919. 

One to five stars along either the left or right edge of the plate. 

Solid tire motor vehicle (usually a truck) 1914-1917; truck regardless of tire type 1918-1919.  1914 and 1915 plates had a metal band affixed that had the stars on it; in subsequent years, the stars were embossed directly onto the plate, but in some cases these also have a metal band with a different number of stars than on the plate itself.  1914-1916 plates all had all-numeric serials; 1917 plates all had an "S" prefix (presumably for "solid tire"), and 1918-1919 plates all had a "C" prefix (presumably for "commercial"). 
(1915: plate owner unknown) 

All-numeric serial formats, with a blank space along left side. 

Plate originally intended for a solid tire vehicle, but issued instead to a pneumatic tire vehicle (usually a passenger car).  Only issued in 1914 and 1915.  The state over-estimated the number of solid tire plates they would need, and apparently issued the leftovers without the band of stars to pneumatic tire vehicles. 

Small 4 1/2 inch-high plate with all-numeric serial. 

Motorcycle.  All 1914 and 1915 plates had serials with a single leading zero; subsequent years did not. 
(Francis plates) 

Plate number 000. 

Sample plate.  Earliest year seen is 1925. 

Other all-numeric serial formats. 

Passenger car; number of digits varies. 

Serial formats with a single letter prefix A, B, C, D, E (1928-1929 only), or F. 

Passenger car. These were issued after plate number 999-999.  One new letter prefix was introduced each year, 1924 through 1929.  Prior to 1928, the "E" prefix was used on tractor plates. 

Serial formats with a single letter prefix E (1924-1927 only). 

Farm tractor.  In 1928, the "E" prefix was needed for passenger car plates, and tractors instead used a "TE" prefix. 

Serial formats with a single letter prefix H or O. 

Bus or taxi.  There's conflicting information whether "H" was used for buses and taxis for hire and "O" was used for omnibuses (buses not for hire), or vice-versa.  I would guess the former.  The full-sized "O" on 1924-26 plates looks like a lead zero, but it's not. 

Serial formats with a single letter prefix R, S, T, U, V, W, Y, or Z. 

Truck.  The letter prefix was a weight class code, with "R" indicating the lightest trucks and "Z" indicating the heaviest trucks. 

Serial formats with a single letter prefix X. 

Dealer. 

Serial formats with a two-letter prefix TE. 

Farm tractor; only issued in this format 1928 and later.  Identical in appearance to the 1930 plate shown below.  1927 and prior farm tractor plates used a single letter "E" prefix. 

Serial formats with a two-letter prefix TT. 

Trailer. 
(1929:  Moore photo and plate)

Serial formats with a two-letter prefix TX. 

Farm tractor dealer. 

Serial formats with a single letter suffix R or S. 

There's a lot of specualtion about this plate format, but I'm convinced that R-suffix plates, at least, were used for trucks in weight class R after plate number R99-999 was issued.  I've observed R suffixes on 1924 through 1926 plates.  1927 R-suffix plates have been reported by others. 

S-suffix plates are even more of a curiosity.  The obvious, but perhaps incorrect answer is that they were used for trucks in weight class S after plate number S99-999.  However, another plate historian has reported he's uncovered evidence that these were used to designate state-owned vehicles in 1924.  Only 1924 S-suffix plates are known to exist.  State-owned vehicles had the word "Official" stamped on them from 1926 forward.  It's unknown how state-owned vehicle plates might have been designated in 1925. 

Serial formats with other single letter prefixes or suffixes and low numbers. 

Letters J and L have been observed on 1928 plates.  Possibly the letters J and L stand for Judiciary and Legislative, respectively.  Plates with these actual words stamped on them are known from 1929 through 1935. 

Small, 8 inch by 4 1/2 inch plate with all-numeric serial which does not involve a leading zero. 

Regular motorcycle. 
(Francis plate) 

Small, 8 inch by 4 1/2 inch plate with serial formats where the the first character is either a zero or the letter "O". 

Unknown type.  Possibly a motorbike or a commercial motorcycle. 

Small, 8 inch by 4 1/2 inch plate with serial formats using a single letter prefix X. 

Motorcycle dealer. 
(Bergan photo / plate) 

All-numeric serial formats. 

Passenger car. 

Serial formats with a single letter prefix O. 

Bus or taxi.  The "H" designation used on some bus plates was eliminated after 1929.  The letter "H" was just one of many letters used for passenger car plates starting in 1930.  "O" plates continued to be used for buses and taxis. 

Serial formats with a single letter prefix T followed by a number with four or fewer digits. 

Trailer. 

Serial formats with a single letter X in any position. 

The easy answer would be that this is a dealer plate.  However, that would contradict the information below regarding some plates with two-letter suffixes being dealer plates, at least for 1930 and possibly also 1931.  There's a much higher likelihood that "X" plates were used for dealers in 1932 and 1933.  So what are the 1930 and 1931 "X" plates if they're not dealer plates?  I'd guess passenger car plates, but I just don't know. 
(Morrison photo and plate)

Serial formats with a single letter (other than those above) in any position, with zero to four numeric digits in other positions. 

Passenger car. 

Serial formats with a single letter prefix R, S, T, U, V, W, Y, or Z, followed by a five-digit number. 

Truck.  The letter prefix was a weight class code, with "R" indicating the lightest trucks and "Z" indicating the heaviest trucks.  Issued in 1932 and 1933. 

Plate number PA00. 

Sample plate. 

Serial formats with a two-letter prefix TE. 

Farm tractor. 

Serial formats with a two-letter prefix TX. 

Farm tractor dealer. 
(Birkmire photo and plate)

Serial formats with two adjacent letters (other than those above) in either positions 1 and 2 or positions 2 and 3, with zero to three numeric digits in other positions.  In other words, formats xx, xx0, xx00, xx000, 0xx0, and 0xx00. 

Passenger car. 

Serial formats with a two-letter suffix, formats 00xx and 000xx. 

Truck and possibly also dealer.  Issued in 1930 and 1931.  1930 plates in this format with first letter "A" through "V" were truck plates.  By one account, 1930 plates in this format with first letter "X" or "Y" were dealer plates; however, I've never seen one of these.  1931 plates in this format have been observed with first letters "A" and "B"; the usage of such plates is unknown.  My guesses are that they're either R-class truck plates issued after other R-class numbering formats were exhausted, or else they're dealer plates. 

Serial formats with two non-adjacent letters (first letter is R, S, T, U, V, W, Y, or Z). 

Truck.  The first letter was a weight class code, with "R" indicating the lightest trucks and "Z" indicating the heaviest trucks.  The first letter was not necessarily in position 1.  Issued in 1931. 

Small, 4 1/2 inch-high plate with all-numeric serial which does not involve a leading zero. 

Regular motorcycle. 
(Francis plate) 

Small, 4 1/2 inch-high plate with serial formats where the the first character is either a zero or the letter "O". 

Unknown type.  Possibly a motorbike or a commercial motorcycle. 

Small, 4 1/2 inch-high plate with serial formats using a single letter prefix X. 

Motorcycle dealer. 

Small, 4 1/2 inch-high plate with serial formats using a single letter prefix other than those listed above. 

Those with prefix letter "C" might be commercial motorcycle plates or regular motorcycle plates.  Other letters are probably regular motorcycle plates.