Apologies to Transport for London.
In London the Oyster smartcard ticket must be "touched" on a reader to open Underground station ticket barriers. For pre-pay Oyster cards, this is particularly important for calculation of the appropriate fare, so even if gates are open or non-existent (with there only being a small validator), then you must remember to "always touch out".
If you use a browser that complies with modern standards (basically Mozilla, Firefox, Opera etc. - sorry, not Internet Explorer) then this symbol shows up next to any offsite links just to let you know that clicking on it will take you away from alwaystouchout, so you might like to open it in a new tab or window (because obviously I don't want you to leave this site!).
These are areas affected by a particular project. "London" refers to Greater London.