[c#] Regex for 1 or 2 digits, optional non-alphanumeric, 2 known alphas

I've been bashing my head against the wall trying to do what should be a simple regex - I need to match, eg 12po where the 12 part could be one or two digits, then an optional non-alphanumeric like a :.-,_ etc, then the string po.

The eventual use is going to be in C# but I'd like it to work in regular grep on the command line as well. I haven't got access to C#, which doesn't help.

^[0-9]{1,2}[:.,-]?po$

Add any other allowable non-alphanumeric characters to the middle brackets to allow them to be parsed as well.

^\d{1,2}[\W_]?po$

\d defines a number and {1,2} means 1 or two of the expression before, \W defines a non word character.

^[0-9][0-9]?[^A-Za-z0-9]?po$

You can test it here: http://www.regextester.com/

To use this in C#,

Regex r = new Regex(@"^[0-9][0-9]?[^A-Za-z0-9]?po$");
if (r.Match(someText).Success) {
   //Do Something
}

Remember, @ is a useful symbol that means the parser takes the string literally (eg, you don't need to write \\ for one backslash)