Translation / General movement
Use the empty at the bottom of every sign's post to change the general position of the sign.
Adjusting the position relative to the post
On some signs you are able to move or rotate the "top part" of the sign relatively to the sign's post. Use the empty near the "front" to adjust it.
Changing text and imagery
To change the name of the street on some signs, just select the text-object and press tab like you normally would. Then use the empty (selected in the image below) to adjust the sign's length.
The imagery on the signs can be adjusted in the "SETTINGS" frame of any sign's material "SignXX_front"