Plaques are not commonly installed on guitars and as a professional Luthier in a busy shop I've never seen one on a guitar in 15 years of doing this.

Nails would not be a good idea depending on the instrument and it's construction. Nor is affixing to the belly region IMO either as g*bson does it, that's a tone sweet spot on a guitar and not to be messed with or encumbered by swag and such.

What is it that you are trying to achieve?

Apparently the ES345, like the 335, is a semi-hollow body. It has a solid section in the middle, so you could nail a plaque there if you absolutely wanted to, as Gibson does on the Marcus King model, although why you'd want to . . . As for affecting the tone, there's not much tone comes out of a semi-hollow body.

That's really helpful information; thank you! I'll avoid any modification that negatively affects tone.

I was curious about the practice because I'd never seen it before, and was thinking of different ways I could personalize my guitars.

Only seen it once. A J45 with the original finish sanded off (who knows??) came into the shop. Someone had attached an old brass Gibson case tag to the headstock with some small nails presumably to replace the decal that was sanded off. I wouldn’t recommend that one LOL.

One area of personalization that I see is the truss rod cover. On a g*bson Lucile there is a brass cover with engraving and if you like a hardware store of metal objects on a guitar it fits the bill.

Anyway good question and welcome to the form too!