tl;dr: You're fine saying "we repair Macs"
As an member of the Apple Consultants Network, I had to do the guideline and trademark quiz. Here is the
link.
Here is my non-lawyer-don't-hold-me-to-it understanding
1) You can advertise your work on Apple computers, Macs, or Mac. You don't have to put the ™ or anything there.
You cannot
1) Use the Apple logo in any way shape or form. I can't use it unless it's directly next to my designation as an ACN or a Apple Certified Support Professional. The logo must be directly next to the word Apple and can't be used without it.
2) Cannot use Apple or Mac in your business name so "Dave's Mac Repair" won't fly.
3) Imply in any way that you are associated with Apple, doing warranty work for Apple or are endorsed by Apple.
4) Sell anything with the Apple logo or imply you do so. Service - yes. Parts - no.
What's the risk? Not much. I was in a dispute with a local provider implying that he was an AASP and had a few run ins with Apple legal on this. I had to send them a letter than they were abandoning their trademark in Kansas but not pursing this person. They eventually sent a cease and desist letter. Apple will aggressively protect itself on products more than service. If you sell things online, they'll pursue it.