@i and @s are invalid drush aliases

In general, Drush reserves words beginning with the @ sign to indicate that the parameter in question is a site alias. Today, the @i and @s aliases happen to work; however, the command drush @i fontdeck could be ambiguous, as the alias @i would take precedence if it existed.

Aliases beginning with "@" are unsupported behavior, and are not guaranteed to work in the future. It would be advisable to remove the aliases containing the @ character, and rely only on the simpler, conforming variants fyfi and fyfs.