Do your DOT MC numbers have to be a certain size?

Only Name Dot # with no periods for exampleDOT####### And Truck #

 

Chrome is ok as long as it contrasts with color however chrome tends to fade quick. My letters are almost illegible have been earned twice .... that reminds me

 

Driving i81 today and saw a handful of trucks running with what appeared to be no visiable dot/mc numbers or business name.

1st truck was a white and orange w900 pulling what appeared to be an enclosed luxury car hauler. (No name or numbers).

Second was a stretched pete pulling a van trailer with unbroken seal. (No name or numbers)

3rd was a yellow lwb pete pulling a matching trailer and it appeared to have company name and numbers on the frame rail below catwalk. Didnt realize this was a legal option?

Is there something I am missing here, what gives?