Currently, mIRC will not be able to parse the $nick in somealias and will return null.
Uh no, mIRC does handle the $chan $nick $address $fulladdress $site etc identifiers, Just not the text itself, and not through a /signal.
alias somealias { echo -a $nick $fulladdress said $1- on # }
on *:TEXT:*:# { somealias $1- }