This is why you may want to avoid stickers on your treasures...

The unsightly stain on this baseball is from the adhesive from an authentication sticker. This isn't a knock on those services... but it is a good reason to avoid putting stickers on your items -- especially vintage items! 

Zarelli Space Authentication does not place stickers on items. Because all of our Letters of Authenticity feature a large photo of the signature, and we do not issue "card COAs" that don't have photos, there is no need to place a sticker on an item.

In my experience, space collectors avoid official NASA lithos and photos that have stickers on the front. So, not only can it stain an item, it kills the desirability.