The reason they say "motorcycle use only" is because the packages he got are H4. H4 is technically a motorcycle bulb designation, but physically is very similar (and in most cases exactly the same) as a 9003 bulb. 9003 (aka HB2) is the automotive designation for this bulb, and is thus subject to regulation under FMVSS108. Since the bulbs he bought are H4, technically they are illegal. But realistically, it won't matter.

If you have a 9003 bulb, the packaging will not say anything about "motorcycle use only."

I was also disappointed with the 9003 Silverstars. They look just like Cool Blues. My bro's gf has them on her Kia. She had Cool Blues before, but on burned out. My bro bought the 2-pack Silverstars. He replaced the burned out one with a Silverstar. He called me outside and said, "Guess which is the Silverstar." I guessed wrong. User EliteAccord has pics that seem very white, but photographs can be misleading due to white balance settings and monitor settings.