I have a number of different labels and even sheets that I apply to the backs of my pieces. The wording and sentiments reflect the nature and size of the beast. Here's the Avery Label I put on the backs of canvas pieces up to about 30 x 72, which can still be supported by wires. It's tempting to get wordy on those labels, but in the interest of having the information actually ingested I keep it terse.
edit...whatever else, your label should definitely nay-say those adhesive backed hangers, which are the only hangers available at my local Walgreen drugstore and are guaranteed to drop anything weighing over 2 lbs within a few months, if not from adhesive failure then from the delamination of the wall paint. The labels for my largest pieces talk about wall anchors.