Figuring out Trailer plates is a work in progress. Information provided here is a working theory.
First Issue 1926?, most likely earlier, possibly 1921; issued as single plates only
Era 1920's?-1945? :
S-prefix for pneumatic tire (air filled)
T-prefix for solid tire
1926 red/white
1927 green/white
1930 "IODINE" vertically on right side white/black
1935 "APRIL 30" top or "OCTOBER 31" bottom
color variations: red/white; white/red; black/white; white/black no rhyme or reason known as to color variations
1936 black/yellow
Unknown when S and T prefix ended. Weight without letter prefix were trailer 1937? to 1954?
1944 believed to be a full-size plate (not a strip like passenger)
unknown list of all weight classes
1945 yellow/green
1947 black/yellow
1951 white/black
1953 black/yellow
Weight in tons stacked, with "TRA" stacked 1954?-1960?
unknown list of all weight classes
1/2 year known
1955 black/white
1956 black/yellow
1957 white/blue
1958 blue/white
1959 white/blue
Era 1961-1984
Stacked "TRL" prefix
1961 white/red
1962 red/white
1963 white/green
1964 white/black
1965 black/white
1966 white/blue
1967 blue/white
1968 white/black
begin reflective letters
1969 white/blue
1970 white/green
"1670 300 YEARS 1970" bottom
1971 white/brown
1972 white/black
1973 white/blue
1974 white/green
1975 white/maroon
1976 blue/white
1977 red/white
1978 green/white
1979 black/white
1980 blue/white
1981 red/white
1982 green/white
"EXP DEC. 31ST 82" top
1983 black/white
"EXP DEC. 31ST 83" bottom
1984 blue/white
"EXP DEC. 31 84" top
Era 1985-1988
"TL" prefix
1985 red/white
"EXP DEC. 31 85" bottom
1986 green/white
"EXP TRAILER 12/31" bottom
1987 black/white
"EXP TRAILER 12/31" bottom
1988 blue/white
"EXP TRAILER 12/31" bottom
1989-1990 red/white
December passenger sticker; 89 non passenger sticker; 90 passenger sticker
1991 black/white
December passenger sticker; 91 non passenger sticker
1992 no issue; expiration change 12/31/91 to 3/31/93
1993 blue/white
"EXP TRAILER 3/31" bottom
1994 red/white
"EXP TRAILER 3/31" bottom
1995-2015 green/white
passenger month/year stickers
2016-present passenger sticker
First Issue January 1, 2016. Replacement of previous design upon expiration through 2016
