Which is grammatically correct as a sign?

Question

Sevens Heaven, Seven's heaven, Seven's Heaven

Seven refers to a wedding date

Answer 1

If Seven is referring to a wedding date, and you would like to denote that that day is going to be your version of Heaven, Then perhaps using the apostrophe would be the best.

An apostrophe can show possession or can be a contraction.

Seven's Heaven = Seven Is Heaven

Seven's Heaven = Heaven 'belongs to' Seven (possession)

So in this case, using the apostrophe really describes the day quite well in both senses!!!

Good luck on your wedding!!!