Noooo ! Please don’t use clear nail varnish – it is only intended to last for a few days and is usually made of cellulose nitrate or similar. It will deteriorate, darken, crosslink, shrink and become acidic. It is not safe to use on objects and may make numbers unreadable in a few years.
Paraloid (Acryloid) B72 is a copolymer of ethyl methacrylate and methyl acrylate and is extremely stable. It is a Feller Class A polymer, meaning it should remain substantially unchanged (colorless, transparent and soluble in solvents) for at least a century. You can buy it from a variety of conservation and paint suppliers as dry beads which you mix up to a 20% weight/volume solution (20g resin to 100mls acetone). You can keep it in a clean glass jar with a solvent-proof lid.