Regarding Verlys signiatures, generally an incised (scratched into the surface) diamond point signiature is associated with US production, French glass having a moulded signiature, pressed into the glass during manufacture.
There are a number of exceptions, however. Firstly early French Verlys glass, the blown, internally decorated wares produced from the mid 1920's, are signed in diamond point, usually with a model number as well. Likewise, some later mould blown art deco French pieces are seen with a diamond point signiature and I have seen some examples completely unmarked.
The French mark is moulded in relief, usually in the interior centre of bowls & vases. I have pieces marked variously 'Verlys France' 'A Verlys France' and just 'Verlys'.
Some Verlys patterns produced in the US also bear a moulded signiature. US examples of the thistles bowl, for example often carry a moulded 'Verlys' mark to the centre, with or without an additional diamond point signiature to the underside. I also have a US made opalescent Cabochons/ gems vase which carries both a moulded and diamond point incised signiature.
There have been a number of reissues of Verlys bowl patterns from old moulds. These turn up in France quite frequently but are usually easy to spot as they are poorly finished and show an uneven 'orange peel' or crazed type surface resulting from the use of an old and corroded mould. there have been quite a few on the French ebay site recently. Because they come from an original mould, however, they do carry a moulded Verlys mark. The reissues are to my knowledge, never frosted/ satinised as was a great deal of original Verlys.
The best way to determine if the bird is genuine is to refer to the Verlys catalogues. These have been reprinted in two books, Verlys of France and Verlys of America, both by Wayne & Carol McPeek. They are no longer in print but turn up on US ebay fairly frequently. If you post a picture of the bird here, I might be able to identify it, though i don't have the full catalogues as yet (still trying to track down the McPeek books).
I hope this is of help,
Steven