Computercraft website is down so I am bug reporting here...
I hope my error report is in the correct format. either way, I'm sure you'll fuigure it out.
I will also put this report on the forums when I notice the site back online.

Versions
Computercraft version 1.64pr4
minecraft 1.7.10

Action:
Executing any turtle.place(), turtle.placeDown() etc.. command with or without a string in the parameters, with a vanilla sign in the selected turtle inventory slot on any type of turtle.

Expected outcome:
Turtle successfully places a sign with any sting in the parameters.

Actual outcome:
Minecraft crashes. Upon restarting, a blank sign is placed and the turtle's inventory remains unchanged.

Crash report:
http://pastebin.com/raw.php?i=hfpgfgx8

Fixed in 1.64pr5