This may sound a bit silly, but my husband and I have a simple signal we use for kissing.  When my husband wants me to give him a kiss, he'll kiss the air two times, just loud enough for me to hear and when I want one, I'll do the same.  We do it so often that it has become an automatic thing to kiss when we hear that sound.  It's a very simple way to be reminded of our love for one another.