Script works but I probably misread what your input string would be from the on snotice event, I'm not even sure that you would need that event as the only thing you have shown here is a message sent from chanserv on some channels.
You can see the regex working here, but it then depends on your input, if you even need the snotice event or some on text event instead: https://regex101.com/r/YTrccL/1

That being said, mirc scripts are of course not suited for this task and writing a custom module or using the one already existing for your IRCD would be far better.

#mircscripting @ irc.swiftirc.net == the best mIRC help channel