These have been around for a while, but I've only just come across these Love Heart stamps by SuckUK.
SuckUK's website). This 3-in-1 stamp lets you stamp your own Love Hearts anywhere and everywhere you like (I'm planning on attacking post-its, my calendar, people's faces...)
The three messages read 'call me', 'love you' and 'smile'. I'm not sure how much use I'd get out of the 'call me' stamp, but I think the others are quite sweet.
I think these would be cute on little notes, maybe to jazz up the 'please could you put some washing in' or 'please remember to feed the cat' notes and take the edge off the nagging tone..? :)