Time travel is done by implanting a small chip, called a Tempus into the user. It usually leaves a mark and is often covered up by an hourglass tattoo. The chips need recharging every thirteen uses.

Once someone's chip has been implanted, it bonds to the skin, muscle and bone, literally becoming part of the person. It is near impossible to remove and is extremely expensive and painful to do so. Someone would need permission to get that done by the Creators.

The chip is the size of a fingernail and is transparent, nearly invisible.
The hourglass tattoo is larger, half the size of medium sized hand's palm. It has a black circle surrounding it and is a pretty basic design.