Is it permissible for a husband to hold his wife's hand and kiss it in the street, and is refraining from that considered a custom, or is there a religious proof for it?

This behavior is a breach of decorum and a sign of indecency, as it is considered direct interaction with one's wife in public, and should be avoided. Affection can be shown in other ways, and when alone, one may do as they please, within what is permissible.