You might feel differently if you were the random gas station owner hit with a 400-dollar fine.
Since you feel so strongly about it, you should volunteer to pay it for them.
Doesn't it sound a bit like there may be a division within BP, where some of the retail location managers are *not* removing the stickers to HQ's liking? It seems that way to me, because ten minutes with a plastic putty knife is all it takes to remove the stickers in question. The employees have to go out there to reload receipt paper rolls and empty trash bins anyway, so the "added workload" argument is a bunch of nonsense.
If the franchisees want to spit in corporate's eye, that's on them - let 'em pay. At the current pump prices, that fine won't sting for very long.