There's only three things you can do. One is to prevent theft in the first place. Two is work hard to get your stuff back. Three is to let it get stolen and do nothing about it so some crackhead can sell it for 20 dollars and go smoke a hard earned rock.
Prevent the theft
Locks keep honest people honest. They won't stop a determined or professional thief. That said, leaving your welding equipment in an unlocked garage or shop is begging to get it stolen.
If possible, set up shop near your home or in view of others. Nothing stops burglary and theft as well as real people keeping an eye on the stuff.
Avoid putting your equipment in a building where any entrance is not visible to occupied homes or a busy street. A potential entrance out of sight leaves them with all the time in the world to quietly break in.
If this is unavoidable, a cheap alarm system and monthly monitoring is a big plus.
Meth heads don't care that copper is down. They'll cut your cables anyway... if they can get to them. Take a few hours and make a locking box to wind your cables into.
You guys that have pipeline rigs... people are watching you and they want to steal your truck! All they need is for you to take your eyes off it. They know you work from dawn to dusk and when they see your truck parked at the Hotel, they know you are dead tired asleep.
Funny thing is, the Hotel people aren't watching your rig. In fact, the only person watching your rig are the guys that go around stealing and stripping them. This is what alarms are for. You will sleep through your truck starting and driving away, but the alarm gives you a chance to wake up and stop it. If it gets down the road, it's gone. Use a remote fuel shut off or a remote control battery shutoff. These countermeasures won't stop them, especially if they tow it... but if they are trying to boost it, it just makes it take longer and increases the chances that they will get caught in the act.
Don't show everything off
Don't let passers by see all your cool welding equipment. The entrance should be in sight, but keep the equipment OUT OF SIGHT. A thief has to know there are high dollar items present before the take the trouble to steal them. This is called "security through obscurity." Out of sight, out of mind.
Make sure your full name and phone number are all over everything
Put your full name, address, and phone number including area code all over everything of value, even small items. NEVER put your social security number on it because it doesn't make it immediately clear that it has been stolen because people don't associate you with your number, and it just gives the thief what he needs to also open up a credit account in your name.
If a thief is caught in posession of your stuff, your name and phone number makes is clear that it is YOUR stuff, not theirs, and raises suspicion for an officer to further investigate. They might even place a call to your number to double check to see if they have a legitimate reason to have your stuff.
RECORD THE SERIAL NUMBER!!!!!!!!
This cannot be overstressed! If your stuff was stolen and you don't have the serial number, don't even bother calling the police because there is nothing they can do. It won't even be "hot." Thieves take stuff to pawn shops knowing that they'll walk out with cash because the property hasn't been reported stolen yet (they often steal at 5-6am and sell at 7-8am to the pawn shops) or that it cannot be properly reported because so many people fail to record the serial number!
Report theft immediately
Make sure your stolen property is entered into the NCIC database ASAP. Only a police officer can do this, and they have to have an official report to do so.
In NCIC, there is a data field for other identification numbers (other than serial numbers) Have the officer enter the phone number you wrote on your stuff.
If someone is caught with your property, crucify them! This may sound easy, but unfortunately it's often someone you know... an employee, and uncle, a nephew.
If you let them get away with this, they will steal from you again. I have seen this over and over again like a broken record. It only stops when they go to jail, flee town, or die from their drug addiction. I have seen all three outcomes... taken the collect call from jail... talked to the police when they came looking... and went to the funeral. And I can tell you that especially if they are family, jail is the safest place for them and if you don't send them there, you may live to regret it.