As we all know, the Question mark in IOS is used as interactive help, but what about a ? in a password?
This could for example be a task in your CCIE Lab or at least in on of the many preparation labs.
To use the ? literal just enter crtl+v and then ?
Rack1SW3(config)#username cisco password SECR? LINE <cr>
Rack1SW3(config)#username cisco password SECR? Rack1SW3(config)#
Easy stuff but good to know!
Of course the ? can also be used in ACL Names, Route-maps, etc…