Discussion Forum—A Way with Words, a fun radio show and podcast about language

My step sister, who is a teacher in Connecticut, recently posted an anonymous note from one of her students that used "<3" instead of an actual heart ♥.
Now obviously this is informed by the proliferation of computers and the internet, and their early adoption by young people into computer and internet culture.
I find it amusing and somewhat telling, the effects of the internet that I'm seeing on the real world. Mind you these are 6 or 7 year olds here, so I doubt the use was ironic.

Is there a name for this phenomenon of a symbol or shortcut overtaking the original meaning? I feel it's in the same vein as "atm" no longer having connection to   "automatic teller machine" in many minds, atm now just means atm for many. This is even an extension of that, a symbol of a symbol becoming more popular.