The 377 to Brighton that I was on Sunday, in first class (having paid to upgrade) really didn't have much in the way of signs to tell you. Wish I'd taken a photo.
Basically, the seats all had the antimacassars which are clear. Fine when there are empty seats so they're visible.
The windows had NOTHING. The only sticker was the standard yellow triangle about not having a valid ticket - not specifically related to first class. ONE sticker on ONE side of the compartment.
The doors DID have stickers. Four of them (round grey stickers with 1ST) but being quite light grey, you could miss them. I don't defend those who decide to upgrade one bit, as plenty did on our trip home, but will defend those who could genuinely and honestly miss something they're not specifically looking for.
There was also just one sticker that DID say about first class and the chance of prosecution, but it wasn't in a position that I'd have considered sensible. It's a stark contrast to the 365s where there are so many stickers, you can barely see in to the compartment - although I think there are fewer on the refurbished stock. Over the years, First did get rather carried away with stickers on the 365s.
Anyway, I can see the potential for confusion and can't understand why the TOCs don't just make things clearer. Then there's no hassle in coming down hard on people, and no chance of people winning appeals.
I've said elsewhere that I've been on a 317 where there wasn't a single sticker, and some ex LM-321s have also had one or both compartments without stickers, presumably awaiting the fitting of new ones after the old ones were removed, or possibly following a deep clean. That's not acceptable and to me, a train with no stickers and just the seat coverings should be treated as standard class.
Even on the 319s, many antimacassars were missing because they couldn't be attached at the top (no elastic like the 377s) and were just stuffed in, basically being held with a small strip of adhesive along the bottom. And even they only had 1ST in light grey on white.