I know you all have some bright red lipstick that you may or may not wear regularly. Bright red...not my color! So grab that lipstick (preferably not your new $20 MAC one) and write your sweetie a little something on the mirror this morning.
Or beat them out to their car and put kissy lips on the driver's side window. You can't tell me they won't be thinking about a pucker when you've cleverly made your mark on their window! (And when they go through 4 car washes to try and get it off :)