Tirmidhi 906 – Marking Of Hadi Animals
For understanding Hadith, please note that Prophet Mohammad saw is not responsible for any thing which has been mentioned in hadith as it has been reported by people. If you read the detailed version of this hadith in https://sunnah.com/muslim:1243a , it appears to me that it is just simple reporting of how he performed his ritual. About putting sandals around the neck, it seems to me as a normal thing perhaps done to prevent sandals from falling down while riding. Perhaps, @UmerQureshi sb or @Irfan76 sb can give a better reply