The creation of an identifier will not change police protocol on stopping a vehicle. In fact, it will likely only serve to further the stigma surrounding mh issues. They already have protocol for mh issues. The fact that he was triggered is never going to change anything in police or medical protocol as we also have a Mental health Act that dictates what happens and in what situation. If his reaction is so acute(violent or aggressive), they will take him into custody and present him to hospital and admit him as (if necessary) an involuntary patient for 72 hrs. There is further protocol in the MH Act but you can avoid all of that by approaching it differently (see below).
I believe your brother's startle response is based on very limited or completely untreated clinical therapy, likely no medications to mitigate acute symptoms. In stead of making a card, I would encourage you now to present him to VAC Case Manager for referral to local OSI Clinic (sponsored by VAC). They can assess and treat him, also the can refer him to residential treatment to Homewood or other facility that treats all the difficult cases. Now a veteran he still has options like peer support in Operational Stress Injury Social Support (OSISS) and there is also a number of online support groups available to him. If this has all happened and no progress, there's something that did no go well and needs to be addressed, AGAIN and AGAIN, and AGAIN until it is resolved.
Sorry if this isn't what you were looking for but I have PTSD, my best advise is to Focus on him and his compliance with clinical treatment, not the reaction of emergency services, they are just doing their jobs. He will get better with treatment, it certainly does not get better without it. good luck.
