Ring of Wrong Writing (3.5e Equipment)
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This is a magic ring. When worn, everything written appears to be different writing in the same language and writing style, to the user. The different writing is consistent with each same writing, even when different people use this ring. Also, when writing, what you actually manage to write is only what it appears when using this ring, when you remove the ring it will appear differently.
Spellbooks, if written while wearing this ring, are usable only while this ring (or a ring like it) is being worn, if wearing this ring while reading a normal spellbook, all the spells are uncastable if prepared in that way, and vice versa. It works the same way with scrolls. (However, as a extra rule, you could define some pairs of spells where the written spell transforms into the other of the pair when used with/without the ring, possibly even defining new spells in this way which are otherwise completely inacessible to any casters/etc!)