If you use LinkedIn on your iOS device, your contacts are saved with a linkedin:// URL. These contacts will sync to your Mac and have the same linkedin:// URL in the contact. Unfortunately there is no LinkedIn app on the Mac to open these URLs so you need a helper app of some kind.
Enter BasilSalad.com’s “Open LinkedIn app”. Download the zip file from http://adib.github.io/OpenLinkedIn/ to your mac and drop the app file into your Applications folder. Start the app and set it to Open at Login. The app registers itself to handle the linkedin:// URL and redirect it to your default browser. From now on you’ll have access to the LinkedIn profile for your contacts!