I used to number my tap lines with a sharpie but it would come off when I cleaned them with blc and a pump. I tried stainless tags for $7 for 10 and they work great.
https://www.amazon.com/dp/B0D793QBJ2?ref=ppx_yo2ov_dt_b_fed_asin_title
https://www.amazon.com/dp/B0D793QBJ2?ref=ppx_yo2ov_dt_b_fed_asin_title
