If a sign is imported from 1.7, 1.6, 1.5(possibly lower, only tested down to beta 1.8) to 1.9(couldn't say every single snapshot, but was in every snapshot I've tried) A sign will only use the first word on each line. For Example,

1.7.#, 1.6.#, 1.5.#, etc

Lorem ipsum
dolor sit amet
consectetur
adipiscing elit

1.9 Snapshots

Lorem
dolor
consectetur
adipiscing

Versions Tested on:
1.8, 1.7, 1.6, 1.5, 1.1, 1.8 Beta