Having such an ID card mentioning the condition and "how to handle" instructions would be useful for a condition like epilepsy - where life threatening fits happen suddenly. However, AS doesn't have such things. Thus, the disadvantages outweigh the advantages.
Having an AS ID card is almost as good as putting a sign on your face saying "Aspie" or openly telling everyone that you are one.
The advantages would be better marketing of skills, assuming public awareness and confidence of Aspie obsessive interests is high (not happening soon). You could perhaps include there like "highly skilled in XXXXXX skill". But however this would only apply a small percent of the time.
The rest of the time, it would probably attract unwelcome attention.
I know I'm not PC here, but just because the law (in your area, not mine) somehow includes some clauses for protection of Aspies doesn't mean that people won't hate one. And no matter what the law says, hate will always find a way to manifest.
On the other hand, this could also be abused and these buggers give us a bad name. Just think of all those SOBs who manipulate the system to get welfare benefits (or to slack off during conscription in my country), including things like faking all manner of mental illnesses like depression and so on. Do the rest of the public know better? No. Even if they did, they usually don't have the time to make a proper diagnosis and they tend to generalise.
Even putting AS on an identity card with "handling instructions" might have negative effects. People would lump AS together with conditions like say epilepsy or something that can flare up immediately and unpredictably. Then they have more perceived reason to shun AS people.
So, I don't think this is a good idea.