Many Pokémon now have Signature Moves that are made for them, that soon are given to other Pokémon. It sometimes seems a bit unfair, but the Pokémon that get the moves also make sense. There are also some Pokémon that could use their own Signature Moves or a Signature Move of another Pokémon. It does make the moves a bit less special, but a lot more known. If you could think of any Signature Moves for Pokémon that could eventually come out, for a Pokémon that doesn't have one, or to give a Signature Move from one to another, let's discuss it.
The earliest signature move I can remember is way back in generation 2. Specifically, Heracross's Megahorn attack. A powerful physical bug-type move that was eventually given to other Pokémon as the series progressed, especially since the physical/special split from Gen 4. Megahorn has since been given to a large majority of physically strong, horned Pokémon, like Nidoking and Rhyperior, so they have more coverage against types they may be weak against. Heracross didn't seem all that special anymore until Mega Evolution came about, but that's another topic entirely. As for Pokémon that are in need of a signature move... I'm not sure. The starter Pokémon of later generations each got their own signature move, but the earlier ones from gen 1 and 2 did not. I think they at least deserve something of the like, Mega Evolution or not. But that's just my opinion.
I don't really have a specific problem with any particular signature move, but I admit I'm not usually a fan of that kind of direction, I think if something was meant to be signature, its should stay so. Not that I'm going to get up in arms about it though, it's minor on my horizon