Much like Dallas keys, magnetic swipe cards can be allocated to clerks and used to restrict access to programming and reporting modes.
ID swipe cards be customised and printed to your specifications with your company logo etc.
In order to use these cards you will require a magnetic swipe reader or MSR, these are usually only available with high end EPoS terminals and are usually an additional cost.
Again the only real issue is that an operator could lose their swipe card but this can be resolved by adding a 4 digit sign in code for emergencies.
Another issue is that unlike with a Dallas key (which you remove as you leave the till) once you have swiped your card you will remain logged in until another clerk logs in or until you log out. If you forget to do this then another clerk could be using the terminal with your clerk details.
Also custom printed cards can be expensive and Dallas keys can be a cheaper option.