Lots of tidbits from this Gourmet article about proposing at restaurants and eating out on Valentine's Day. For those who don't have the time, here all the hints:

Don't put the ring in crème brûlée.
Don't put the ring into a salad and then order caviar.
Do have "a special plate with a trapdoor and a secret compartment."
Don't force your date to order a dessert if it's hiding a ring.
Don't paint "Will you marry me?" on a plate.
Don't turn her down at a restaurant if you think she might throw plates.
Don't call the co-owner at home to tell them the engagement is off and not to tell anyone.
Do visit the restaurant a week before and confer with the manager.
Do get seated in the middle of the restaurant.
Do find out what a cloche is because some restaurants use them to hide rings.
Do print a custom with your question under the Specials.
Do ask in advance and have your mother-in-law pay for dinner.
Do sit privately if you're going to ask for a divorce.
Do bring your mistress on February 13th.
Do fill a private room with rose petals, candles, and everything good on the menu if you cheat on your wife.
Do not touch your partner sexually at the restaurant or have sex in the bathroom.
Do stop if asked by a matronly waitress.
Do try to book a six-top at a restaurant on 2/14. That's an easy reservation because everyone is booking as a couple.
Do ask for the manager's help in inviting your 50 closest friends to a shotgun wedding.
Do leave a hotel key in a box for your husband, asking that it be delivered in 5 minutes.