ISO: Blue (usually) Silicone? tape retainer material

[Chuck Guzis]

Another open-reel tape query for the experts.

I recall that new tapes would often come with a strip of (usually blue)
silicone-ish tape to retain the end of the tape.  I've got a couple of
strips here and I'll swear that I've seen the stuff in other
applications, but memory fails me.

It's not sticky in itself, but sticks quite nicely to mylar tape.
Easily removed and indefinitely reusable.

I think I've seen it in kids' toys of the era, where various patterned
pieces were cut from the stuff and assembled on something akin to a
whiteboard.

Does this ring any bells with anyone?  Do you know what the stuff is and
where I can get some?

Thanks for any help,
Chuck