Extracting Word Coming After Number

I have a column with codes coming after a # symbol and want to extract just the code from the cell. The code could be 2 or 4 characters in length. Some examples:

#AA abcdef

From this I would want the formula to return #AA.

#ABCD qwerty

From this, I would want the formula to return #ABCD.

The #Code should but may not always be the first word in the cell, so it needs to find the # symbol and then take the next x characters until a space is found. Note that the reason code may be the only text in the field, so a space may not be there at all. For instance,

#RR

Should just return the #RR.

Edit: This actually has become more complex now. The cell could be

#AA{text}

And for that, I would just want the #AA.

The formula would need to begin at the # and return just the next x capital letters.