Exactly. They just see another piece of bent metal, together with mic stands, cymbal stands, etc, etc and ignore it if the music's any good.
As far as the "learn your parts" comments on here are concerned, that's fine if you play the same 20 songs every night, but if you take requests or have a large repertoire (some items from which you may not have performed for a while), you need parts, words, etc. That's why orchestras, jazz bands, etc, use the dots.