Scavenger's answer is a good idea, but # might be something that is valid in the code, so ti would be better to have something that is specified before the code block in a special way. The code block is indented with 4 spaces, so the language specifier could be indented 3 spaces (and only mean something when appearing immediately before a code block)
VB.NET
Dim myVariable As String 'Here is the first code line
myVariable = "Hello world"