I'm new to this, but in my opinion, signature items have no intrinsic value. Unless you're collecting other people's signature items, they're just something that would be of interest to the cache owner ( to see who has come by, etc.)
I consider leaving signature items as a bonus. Something you'd leave without taking something else. If you're going to trade, trade something of value in addition to leaving your calling card.
That way, a few months down the road, someone doesn't have to open up a cache full of business cards and get disappointed.
Now, if you were going to leave a PAIR of cufflinks, for example, that might be different. Someone might actually be able to use those. But, one... Not too many one-armed men who like to wear formal clothes rummaging around in the woods, eh?