Years ago, in NYC, I used to hide a key in a magnetic key box outside attached to the underside of metal stairs. 

Also, I ordered 2 car magnets that say "I BUY HOMES" and then my number right below it which havent been delivered yet so im still waiting for those. but so far no calls so im trying to get as much exposure as I can.

What I did is created a bandit sign magnet for my car.

However, there is a huge tower 3 blocks away that could be seen anywhere in the neighborhood.It's a cookie cutter neighborhood so many houses nearby do have the same situation.I read that besides being a fire hazard, the magnetic field might cause health issue therefore affects price appreciation.

Pretty much flood my contact list with post cards, door hangers, fridge magnets, yellow letters, etc. 

We close some in our house (in our large closet and unused bedrooms), and I even put a large magnet over them to help seal them where we don't need heat. 

I'm finding that to upgrade to a proximity tag or intercom system type entrance access system for tenants I'll need to replace the doors with something that has the electric/magnetic strike. 

Could my friend also slap on a couple magnets with ads for the LLC and expense the miles driven from/to the LLC home office to/from the “day job” as mobile advertising?

Are you talking about a electro-magnetic field?

Then what collateral is there, the shell with a neon sign, some yard signs, a magnetic sign for your truck, some radio copy, forms, contracts and a phone number?