The new Cheat Key for TTDPatch here same as OpenTTD Cheat Arrow :
Ctrl + Alt + C
Have a look at http://www.tt-wiki.net/wiki/SignCheats
and the page it links to. As I understand it, TTDPatch is limited in the keys it can use for performing actions when combined with a click or other key strokes.
Formerly known as r0b0t_b0y2003, robotboy, roboboy and beclawat. The best place to get the most recent nightly builds of TTDPatch is: http://roboboy.users.tt-forums.net/TTDPatch/nightlies/