Nikkie, if the sign is an accessioned artifact, it deserves the same care as any other object. Therefore, a thorough analysis of its condition is in order before any sort of conservation treatment is initiated. PVA adhesive may be a reasonable material to use, but you have to consider the materials and their conditions that you are dealing with. It may be just the original adhesive for the vinyl that is giving way, but the vinyl itself it considered to be a material with “inherent vice”, such that it degrades over time. So, the vinyl material may be disintegrating; second, the PVA adhesive may be ineffective at re-sticking the vinyl; or, third, the whole attempt may be unsuccessful, creating a sad mess. Even for simple — and presumably low-value — objects, it is essential for those of us responsible for their care to consider all treatment in a professional way. In this case, perhaps store the sign horizontally until a conservator can give it a complete examination, and offer a treatment proposal.