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13.2 Provide metadata to add semantic information to pages and sites. [Priority 2] (Checkpoint 13.2)[w3.org...]
There is no specific accessibility meta tag as far as I know.
No quick fix for accessibility I am afraid. Who ever asked you to find them must habe gotten muddled up.
[diveintoaccessibility.org...]
The above should help you. You dont need to go as far as he does to be legal but there are some really good tips in there.
Once you have passed your site through bobby's tests, you can put a 'bobby approved' icon on the site (see [bobby.watchfire.com...] ), but not even bobby's own site has any special meta tags to identify its accessibility level.