Is it permitted to affix stickers of the moon and stars?

Hello and blessings,

It is permitted [however, manufacturing them is forbidden, because that is considered making them and not merely drawing them, and it is forbidden to make the form of the moon and stars].

However, one should not affix stickers that contain parts of the form of the sun, moon, or stars, where by the placement of the stickers a complete form is created.

Shulchan Aruch, Yoreh De'ah, siman 141, se'if 4; and see Rema there, se'if 3. The same applies here, that it is permitted to keep the stickers, since they are manufactured in a factory and there is no concern that they are worshiped.