I picked up a couple of these collars for my service dog off of Amazon. They are great for the summer because they are way lighter than the whole vest while still being obvious enough to alert the general public that he is a service dog. The part that says service dog also slips off and could be affixed to any collar.

https://www.amazon.com/gp/aw/d/B07RV33LTV?psc=1&ref=ppx_pop_mob_b_asin_title