This i think is not a trello specific issue as i have the same issue on google news.
The icons are showing up as boxes with thin lines on the sides and thicker lines on the top and bottom (if that is familiar to anyone). It seems to be a default place holder image for icons.
Even this typing this issue out on the Ask a Question page the format buttons - Bold, Italic, Underline, etc - aren't showing up properly. The tooltips work so i can hover over the generic icon and see what the icon is supposed to be for.
On google news, the verticle navigation pane has letters (big letters probably 24 font size) in place of the icons that usually show up there, so i can see just part of a few letters.
I'll attach a few screen shots. Thanks for the help. 
