At least as of right now, visiting meta sites over SSL is "not supported". The most recent information I could find on meta.SE was from last year, and there doesn't appear to have been any change since then.
The technical problem is the way the domain names are formatted breaks the wildcard SSL certificates. The certificate is for
*.stackexchange.com, which matches
site.stackexchange.com but doesn't match
In order to make things work they need to restructure the domain names so that, e.g.
meta.scifi.stackexchange.com ===> scifi.meta.stackexchange.com
Once that's done, a certificate for
*.meta.stackexchange.com will work, but I assume that's not a trivial change so they haven't gotten around to it.
Better HTTPS support for Stack Exchange sites
Untrusted connection when visiting per-site meta over SSL
This blog post