squares with numbers inside

[highway star]

I keep seeing strange square things with numbers inside. An example is on Riddlers 'security measure' thread. on Smileyinside's reply after 'very practical Riddler' there's 5 of these squares.
What the heck are they!

 

[AliK]

Ah! I know what that would be!

99.9% of the time I use the iPhone Tapatalk app. If you use the iphone keyboard for adding predefined smilies, they turn up as squares on the website view as your browser won't recognise them.