The retainers look like the type I would make for a flexible face sign. It's hard to tell the scale from the picture. But if those retainers are three inches wide or so, that would point to a flexible face.
Also, when I have put new vinyl on an existing flexible face, I usually did it in place. The face was already stretched and squared up, so why remove it? Trimming the vinyl at the retainer edge does not seem like a good idea, though. But if the guy used cheap vinyl he may have also cut corners on the install, saving time by not removing the retainers for trimming.
By the way, flexible face material is very forgiving to accidental knife cuts when trimming in the field. If you cut through it it does not generally continue ripping. If the cuts are small they may not even be noticeable sometimes. A small cut can even be repaired with the little waterbed repair kits.
There could be a seam in the face but I can't see it.