If you want to change the meta tags of mini-site and signup page, then you can make the desired changes at:
Configuration > Design > Signup page theme > click "Edit theme" on the active theme > look up:
For minisite: static_page_includes.stpl
For signup: panel_includes.stpl
Let's say I wanted to change the title of the "FAQ" mini-site page.
First of all, I would look up the static_page_includes.stpl file in my signup theme and comment out the following line:
So I would simply replace it with:
Now, I would have to open 'faq_public.stpl' via Theme editor in Merchant panel.
and add to the very first line this:
<head><title>My FAQ page</title></head>
That's it ;-)