People put a variety of information in their email signature files, from business phone numbers to favorite quotations to colorful images of their signatures. I recently got an email that had a very clever sig line, as follows:
"I reply to emails at 8AM, 2PM and 4PM.
Calls returned: 10-11AM, 1-2PM and 5-6PM."
Short and sweet, gets right to the point.
If you find yourself constantly interrupted by emails and calls (and can't seem to resist answering/looking at them), try managing the expectations of your correspondents this way. Tack a similar phrase onto the end of your outgoing voicemail, too.