Unknown Green Stamp - Assistance Identifying?

I have tried unsuccessfully to identify this stamp, but with no luck. Search just about everywhere I could think of to try and find out what it is, but am stumped. I am hoping that someone here might be able to assist.

No idea what country it is from, and there is no denomination on it.

Sincere appreciation in advance!

It's not a stamp, but decorative paper from the edge of the sheet. Commonly found on the edging of stamps from France or French colonies.

Thanks! I've been working though a collection of older world stamps from a relative, and I have found the Stamp Identifer app on my iPhone to be fantastic in identify most of the "not obvious" stamps. If the app can't identify it I start googling and ebaying and going to stamp sites to see if I can find it. If that fails, I ask here and the forum is batting 1000 for the few that make it to this forum.

I hadn't thought of this one as possibly just being decorative, but now that I know that the clues are there (no denomination, etc) so nice learning moment for me.

Thank you!

Here are a few more from a page I have. You can see letters such as D, E and G. Possibly I too? They must stand for something...

Institut de gravure?

It's obvious when you consider what a postage stamp actually is: a receipt for or proof of, the sender having paid to send the letter, and receipts have to have certain things to be receipts. The UPU (Universal Postal Union, founded 1874) formalized the requirements for postage stamps, which include the requirement to have both an indication of 1) value/denomination (whether number, letter, written description, QR code, etc), and 2) issuing authority (for most a country name, for the UK a profile of the reigning sovereign). If you come across something without both of those, it likely isn't a postage stamp.