Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.
I would ask the folks at Sailrite (sailrite@sailrite.com). They sell a number of adhesives that would probably do the job. More importantly, they are very helpful and knowledgeable about all fabric questions.
Go to sailrite or call your local loft (IF YOU Have one...(frank that part was for you)) they will get you a new one for a few bucks. They aren't required unless you race the boat, so your other option is just to let it go.
I worked as a sailmaker for a few years and found out that when the numbers are coming off it's likely there are other things that need attention. I would recommend you go to your local sailmaker and have them check out your sail. If the cloth is holding up and stitching is getting weak, you can have the stitching resewn and be back in business for not much money. I recommend having them put new numbers on for you also, it takes a lot of practice to learn how to get those numbers on straight. Even in a sailloft I've seen a fair number of logos and numbers ruined when they were being installed.
Notice: The advice given on this site is based upon individual or quoted experience, yours may differ. The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.