How to Join LinkedIn without an Invitation
Complete the fields regarding your current employment status and location.
Specifically, you need to provide the following information:
Country and ZIP code: LinkedIn won't display your ZIP code, but it does use it to assign a Region to your profile so others know the general area where you reside.
I am currently: Indicate whether you're employed, a job seeker, or a student.
Details about your status: Depending on your status, LinkedIn asks for a Company, Job Title, and Industry if you are employed, or asks for your most recent job title and company, if you're looking for work.
If you find it difficult to choose an industry that best describes your primary expertise, just choose one that's closest. You can always change the selection later. If you're employed but looking for another job, you should still pick the industry of your current profession.