The Wiki is your best friend.
http://online.ts2009.com/mediaWiki/index.php/Main_Page
http://online.ts2009.com/mediaWiki/index.php/Index_of_Tags_&_Containers#qu-rz
rotate-yz-range 
The format for the values is this:
rotate-yz-range       0,0
Where min and max (left, right) are values in degrees. This tag lets you set the roll / yz rotation range (normal object rotation is an xy rotation). If you want your scenery object to support rolling then use this tag to set the minimum and maximum roll range. By default, objects have a min/max roll range of 0 to 0.
What you need to do:
This is done in Content Manager:
1) Clone the sign you want to use. It can't be built-in so choose one of the many gazillion signs out there.
2) Change your CM view to Open for edit.
3) Right click on "New Asset".
4) Pick Open... and Edit Config.txt
The Config.txt will open up in Notepad by default on Windows. Never, ever, ever edit this in Word or some other word processing program, otherwise, you'll have junk and a corrupted file.
5) Add in the above tag.
Put in the tag anywhere except between anything with { } (curly brackets), which create containers. Use the formatting in the config.txt file and match up the alignment.
While you are at it, edit the Username to something of your own. Again, replace the text in there and follow the formatting.
6) When done editing, save the config.txt file.
7) Close Notepad
Back in Content Manager:
8) Right-click on the asset and choose submit.
It will disappear from the list.
9) Filter on Today (meaning the day you are doing this),
Your asset should show up in the list.
If there are any errors, right-click and view errors and warnings. Forget warnings, and look at errors only - the red X things.
If there are errors, repeat the edit again, and fix anything, by opening the asset up for editing again and editing the config.txt file.
This is pretty much the process, which I've put together from memory since I'm not at my Trainzing PC to confirm the steps.