VRE put a V in front of the locomotive numbers during its time under Amtrak to keep the numbers clearly separate from Amtrak's own locomotives. So for example, if they were to call out saying that engine number 24 was the lead unit on a train, they would know that it was AMTK 24, as opposed to V24, which would be VRE's locomotive. I suppose it's probably not necessary anymore, but has stuck nonetheless, and might still be a good idea in the event they need to fill out a Form D, just to avoid any possible confusion.
Also, samshat, I'm upset I didn't check this forum a week ago to read that V55 and V56 were going to be running through here. I would have gone out if I'd expected more than the usual weekend Amtraks... I DID however catch V55 on the P325 the next Monday (21st) heading south at Crestwood:
My apologies that I had to make it black & white - the contrast here is still crap until the leaves come back. I can tell you however that V55 is looking nice and shiny! Hope she doesn't have the same setback that V52 had on the RF&P...