I have this legacy code that I am working with and there is code like this all over the place:
#If PRE611 = True Then \'Do Something #Else
Those are directives, and allows you to do conditional compiling. # sign used for directives.
In this case It will compiled either part of the code based on the evaluation of "PRE611 = True"
You can see this article for some examples : http://visualbasic.about.com/od/usingvbnet/a/vbdirectives01_2.htm
It's a pre-processor directive.
It essentially means if PRE611
is defined as true (in the pre-processor) to compile whatever follows.