"City Icons" created by Adam Whitcroft.

http://adamwhitcroft.com/offscreen/

"City Icons" work is licensed under a Creative Commons Attribution-NoDerivs 3.0 Unported License (http://creativecommons.org/licenses/by-nd/3.0/). Simply put you're free to use the icons in commercial work provided you do not alter, transform or build upon the icons and that you do provide clear attribution.