What does this sign mean on twitter?

[Lai]

i always see this sign on twitter, its a square with little writing inside and i dunno what it means or meant to represent.. example is here: https://twitter.com/snooki/status/205710731579105281 any help? ^.^

[Brad]

I've seen that a few times are do not know for sure; however I reckon it's like a love heart? '<3' or something

[Abby]

I don't see any little square i saw a face. So it's probably emoji. Emoji is like a little icon that you can only see if you have an apple product.