This is expected behavior. This character is the "escape character" used in expressions to tell filemaker "take the next character literally"--not as an operator or other character with special significance.
You can put it in front of quotes \" for example so that you actually get the quote marks entered into the field or variable instead of it being interepreted by the specify calculation dialog as the end of a literal string.
To get both slashes in your expression, escape them with yet another \ (use \\\\ to get \\) or substitute / for \ as they can be used interchangeably in file path expressions.
Like most of the people I know, I'm using an extra table with only one single record, to put logos, fixed values, and so on.
I have for example a field called something like "Tab", filled with a *tabulator*.
I recommand also a field called something like "slash" and "backslash", which you can easely use in calculations.
Thanks. I found a way around it "\ \" and subsitude the " " with the ""