Death stamps and death symbols on Prisoner Registration Card in concentration camps during WWII - Cross build by four 'T' shapes (potent cross) was used to mark the death on inmates cards.

Part of Prisoner Registration Card with hand written mark of death that looked almost like svastikas.

Prisoner registration card from Buchenwald with two potent cross marks..

Enlarged potent cross from the registration card below.

Prisoner Registration Cards. These cards were created for concentration camp prisoners in all of the main camps. At first glance, the cards look very diverse as they come in various colors. They were filled out by prisoner clerks either by hand or on a typewriter, and sometimes by the prisoner. These cards were used for all age groups, nationalities and prisoner categories. There was no registration in the death camps for the groups of Jews that were send to gas chambers after the selection (directly after arrival).
On many Registrations cards one can find kind of marks or stamps composed by 4 'T' shapes, kind of the potent cross. Potent is an old word for a crutch. Similar crosses are known as the "Jerusalem crosses". On some cards there is also 'T'. 'T' comes toten, in German death.

The registration card of Anne Frank with the "Death mark".

The registration card of Margot Frank with the "Death mark" at two places and overwritten letter T at the top.

Does anybody know the origins of the "4 x T" sign or "Potent cross" (here in red) which appears on the documents from the concentration camps?