If this is indeed Aleister Crowley signature sigil. I highly doubt its the actual version. There would probably be a form of security within it so he couldn’t be used in a ritual or bound to a circle.
This illustration is from Crowley’s Book Four: Magick.
I agree with the security mechanisms though: that’s a given.
How would someone actually go about incorporating security into their sigils?
Omit an integral part of the sigil entirely when printing, alter an integral part slightly, place a sigil inside the sigil somewhere in order to protect it etc etc.
Not to mention the countless other workings you can do in conjunction with the sigil otself in order to further protect it/ throw potiential abusers off track.