Currently the information if a secret key is available for a certificate is available via:

• the font, which is by default bold for secret keys
• the certificate details (line "Secret key" and column "Storage")
• using the filter "My own"

To make this better recoverable in the general certificate list for visually impaired people, a column "Key" with the values "secret" or "public" could be used.
The column should be hidden by default and positioned between mail and status.