The context is right there on the trailer.

“Look twice” is a phrase to raise driver awareness of motorcycle safety. Right below it, though kind of hard to see, it says “[MO]TORCYCLES”

Then there’s the Yamaha sticker. They make motorcycles (and musical instruments lol).

Finally, you think some deadly pathogen would just be transported in a flimsy-ass consumer grade trailer? How about some Occam’s razor?

To “cry wolf” is to unnecessarily raise the hue and cry (either on purpose, or through naïveté), something those taking this phrase literally are far more guilty of than the owner of this trailer.

If I say “Watch out, don’t hurt yourself thinking too hard,” that, like the above, would be understood as a joke even though it takes the form of a warning. It’s not my fault if you freak yourself out worrying about literally hurting yourself by thinking too hard.