On Twitter what does a square box mean?  I see 1-4 of them on people's post & I'm not getting it!!!
I think the box shows up when a person tries to use a symbol but it doesn't show up on other users. Generally, people with iPhones are able to write some similes and if you don't have an iPhone you can't see what they saying.
It means it was a re-tweet.
They're called emoji and are meant to show up as nice graphic symbols. If you use Google Chrome, you can enable viewing of these with www.TwitterEnhanced.com instead of just mobile devices.