Mage cuffs, mage mask
^^^
Definitely for a restrain the mage situation!
For a Johnson/Fixer keeping runners in line? Reputation might be a good way to go -- if you make a mess of things using magic, you'll start to be known as that half-cocked crazy mage/shaman. When jobs start dropping off because your too much of a loose cannon, it's not too much different from a street sam known for being particularly aggressive or violent. Only certain types of jobs get thrown their way -- usually with double crossing messy ends!
A Johnson could reward 'good behavior' -- just like the mundane members of a team, if the mage completes the mission discreetly and quietly, the Johnson may take notice. A little extra nuyen and the opportunity to move up the chain to the next higher Johnson. More nuyen, more equipment, perhaps a magical group takes notice of the professionalism and approaches the character. These are definitely not quick security measures - but given time, it will help your magicians grow as well as the entire team.
Now for the quick and dirty --- it's already been mentioned - but wards and spirits are a good start. Even a watcher can report -- usually in high security areas, just knowing magic is active is enough to cause problems. You can use magic all you want - but your meat bod is still behind all those security gates whether or not you are a big bad with magic.
Sentry guns anyone?
Anchored spells - not cost effective, but might be useful in certain situations. Also don't forget about astral signatures -- could lead to someone tracking you down.
One last thought - if the Johnson is big enough and has the team over a barrel for some reason, have them ask for a blood sample from everyone - including a mage. Watch your player squirm then - I was in that situation once as a player and it drove me (and my character) nuts! Until I had the sample in hand and destroyed, I was walking paranoia!!!
