That annoying alert comes up whenever the page is requesting outside data via "http://"
If this is only happening on a page with the map installed, then look for code that starts like this: (it's a much longer string, I am just posting the beginning)
Change the http:// to https://
As long as the google maps api runs from https it should work.
(note: if your page calls other 'outside scripts' via http, they would also have to be changed to https. (ie: flash, facebook, twitter, etc...)