This is an alias that is missing from mIRC for some reason. $utf8(N) will return the utf8 character that corresponds to the number (N).
I also added two examples (flip & octatext) and the alias H2U.
Flip will turn your text upside-down and octatext will print your text in little octagons.
The alias H2U just converts the (N) in $h2u(N) from hexadecimal to base10 before calling $utf8(N).
H2U will convert the hexadecimal number to the corresponding utf8 character.