Is there any symbol for "undefined"? [duplicate]

According to a Wikipedia article on the subject, in Herbert B. Enderton's book Computability: An Introduction to Recursion Theory (2011), even if nowhere else (no other reference is given, and I've never seen the usage):

If $f$ is a partial function on $S$ and $a$ is an element of $S$, then this is written as $f(a)\!\downarrow$ and is read as "$f(a)$ is defined."

If $a$ is not in the domain of $f$, then this is written as $f(a)\!\uparrow$ and is read as "$f(a)$ is undefined".

I have never seen such a symbol. I don't think it would be very useful, and it might make unexperienced people less aware that they are dealing with an undefined entity, and start doing calculations with it getting meaningless results.