Did your waitress draw a smiley face on your last restaurant check? It may have been simple cheerfulness on her part, but it's also a proven way to get a bigger tip. Michael Lynn, an associate professor of consumer behavior and marketing at Cornell University in Ithaca, N.Y., has done scientific studies on tipping and offers these strategies to servers: Introduce yourself; squat next to the table (to make better eye contact); smile; touch customers on the shoulder or hand; write "thank you" on the back of the check; and use tip trays with credit-card logos on them. Note: The "smiley face" gambit is for waitresses only and can backfire for waiters. Perhaps it's too feminine, Lynn says. Waiters might try a more masculine or formal drawing.
Source: 'Seven Ways to Increase Your Servers' Tips,' by Michael Lynn, published in Cornell HRA Quarterly No. 37 (June), 24-29.