Ever tried to remove one of these??

[pirminiamac]

These are staying but I have another on a display tank I want to remove, if my hermit crabs have no luck I don't hold up much hope, they are destruction machines!
Any tips for getting them off without damaging my glass? Is it going to leave a ugly mark?

 

[nykxx]

These should be removable but it might be tough if you’ve had it on there for a while. If you move it and it loses stickiness, I’m sure you can buy some 3M double sided stickies.
I usually use warm soapy water and a razor (or plastic scraper) to get adhesive off

 

[sdsnybny]

Use an electric (hair) blow dryer to heat up the glue from the backside through the glass. That should soften it up enough to pull it free.

 

[Dave Jay]

A razor blade should work, best to use a safety blade or a Stanley knife blade to avoid cutting yourself. An old credit card makes a good scraper too. Glass is harder than steel, so once off you can use steel wool or a scourer to remove the residue without scatching the glass , but keep in mind that while the steel won't scratch glass, dust and dirt can so keep cleaning the blades and wool while you work. If you prefer a natural cleaner rather than dish washing liquid, which I haven't found particularily effective , try lemon juice or vinegar which will work on an alkaline residue, or a paste of bi-carb soda (sodium bicarbonate ) which will remove acidic residue . Between the two you can pretty much remove anything from glass without using any toxic chemicals. They neutralise each other, and rinse off easily with water. Depending on where you live sodium bicarbonate might be sold as bi-carb soda or baking soda, baking powder is not the same thing.
The heating idea is a good one , just don't get carried away and crack the glass.