Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.112.

Ish’ar (or marking) means that a camel or cow to be slaughtered is marked by cutting off their humps on one side. This serves as a mark that they are intended for sacrifice so that no one should cause them any harm.

And taqlid or garlanding means putting a leather piece around the sacrificial animal’s neck to mark it as such.

The Prophet (peace be upon him) garlanded the sheep that he had marked out for slaughtering and sent them with Abu Bakr to Makkah when he performed Hajj in the 9th year after Hijrah. It is affirmed by ahadith that the Prophet (peace be upon him) garlanded sacrificial animals, marked them and doned ihram for ‘Umrah at the time of Hudaibiah. Most scholars, except Abu Hanifah, hold that marking the sacrificial animal is desirable.