The output of a neon sign transformer can definitely kill you, but maybe I got lucky.
When I was in high school, I accidentally picked up my 15 kilovolt 30 milliamp neon sign transformer by the terminals and insulators while it was plugged in. I got as far as lifting it before I consciously set it down and released it rather than dropping or throwing it. The total time was a couple seconds. After that I sat against the wall for a couple minutes sweating.
I have experienced 120 volt AC line voltage a couple of times and I would say that it was worse, but of course then the impedance is lower and the current is higher.
Another time I was working with a 1000 volt DC power supply that I had built for a strobe and managed to short the output out from my finger tip to my elbow while standing on an aluminum ladder. That knocked me off the ladder and across the concrete floor. I had a pair of burn marks on the tip of my finger and my elbow, and my whole arm hurt for days. In this case the power supply had 10s of microfarads of capacitance which was way too much, lesson learned.
safe? i would not call it safe by any means, even a few mA at 12kv will burn you at least
I was not burned but there was no sustained arc.
30 ma at a couple of KV (DC or low freq AC) will knock you across the room from the muscle contraction.(no it does not knock you, your muscles knock you, the result is the same and it hurts). Yes I have empirical data ...
No, I have experienced both and the current limited AC will not. Even 1000 volts of DC can knock you across the room, and off of a ladder in my case, if it has a moderate amount of capacitance or low enough impedance.
By the way, if a transformer is marked "30mA", this is a continuous rating. In the case of a short circuit, (for example through the "low" resistance of an human), it will happily supply 10-50x more -> 300mA to 1,5A.
To these lethal effects of electric current, at that high voltages and high current, the heat of the arc will burn flesh.
The output current of a neon sign transformers is deliberately limited by the transformer's impedance. They could certainly burn flesh if an arc is present, however inadvertent contact will likely result in either immediate recoil or intimate contact. In either case an arc is not present for long enough to burn.