Let's see.... there's a myriad of things which could've contributed to this problem of a sign falling off the door.
When adhering one thing to another thing, certain questions should be asked before giving people instructions on hanging their own sign.
Is it a wood or metal door ??
Is the door painted ??
If so, how long ago ??
What kinda paint ??
Was it prepped properly ??
You'll probably get adequate answers, but the real culprit isn't tape vs. glue or pins, but you didn't explain the most important part. If you are adhering anything to a coat of paint, it's the paint you are expecting to hold that sign up, not the glue, tape or door itself. You are relying on a thin coat of paint to hold your sign. Without physical fasteners, this sign was doomed from the gitgo.
Without knowing what's going on somewhere, where you have no control over the circumstances, you did not take proper precautions to prevent this.
We're doing a day-care center inside and out. The guy just called yesterday to get a buncha signs for the doors. I think 3" x 10" x 1/8" thick. I asked him all those same questions and he said, Gene, I'm a contractor, of course I know I did everything right. I sanded them, primed them and gave them two coats of topcoat. I said, good for you, but without a physical fastener on each side, I would not depend on the tape alone..... not a freshly painted wooden door. He opted for decorative brass screws, in addition to the tape.
