Most of the time it means that they are putting the plate on a 1988 vehicle or that they were born in 1988. But it's being denied because H is the 8th letter of

Most of the time it means that they are putting the plate on a 1988 vehicle or that they were born in 1988. But it's being denied because H is the 8th letter of the alphabet, and thus 88 might be construed as HH, which might be construed as Heil Hitler: https://www.adl.org/resources/hate-symbol/88 https://www.adl.org/resources/hate-symbol/88. In some rare cases it might even be intended to have this meaning.