Valentine cards appeared in the 19C and were elaborate or romantic, comic or rude. Rude ones sent as a joke among the working classes were the cause of the celebration of this day going out of fashion through Victorian times, coming back into popular fashion in the second half of the 20th century. Now the cards are in the shops just after Christmas and everything is sold, from teddies to cakes, with a heart featuring on it and every shop has a Valentine window and florists charge a fortune for roses (cynical ........ moi?).
I found just a couple of weather sayings in my books
To Saint Valentine the spring is a neighbour
Valentine's Day breaks the back of winter
PS. Thank you to all new followers, what a nice surprise.