1. Over 10 recommendations (usually from people who don't matter): This usually means the person has gone out actively to seek recommendations or has asked others to recommend him. Reasons why people do this is that they have been on the job market for a long long time and at the outset are not confident of landing a job as per their expectations. Your eyebrows should esp. go up if you notice the recommendations are from former or present colleagues (former - usually an indication that the person was fired or laid off, present - person has been told to leave and is serving time). I always try and read thinking if the person who wrote was a junior, why would he feel he was entitled to recommend another person unless the person requested it.
2. The person has a large number of groups he has joined and has not participated in any discussions or contributed to the same. It usually means that they are trying to contact as many people as possible during their job search and have very limited real life contacts and so their only means of connecting with other people is to join the same groups as them.
3. You see brand name universities like IIT, IIM, Harvard etc. as part of the qualifications when all the person has done is a certificate program or a Continuing education program from these institutes. This is called 'Resume Embellishment' by recruiters and bullshitting by the rest of us.
4. Vague terms in their profile that seem disconnected with their job title or else their title itself seems Vague and something that no professional company would give them. So you might see Key Member of Management team instead of Vice President or General Manager. Job description may include references to 'opportunities' they created, 'pipeline' they generated or 'potential' business they got or 'revenue/ business they managed'. This is to portray a bigger image of their actual position to recruiters.
5. Connections who seem to have never worked with the person or who seem to be from competing companies. This is a very key flag that I look for. It is a dead giveaway that the person has been interviewing at multiple companies in the industry. Such a person cannot be trusted to not sleep with the enemy in case you apply pressure on them once they join your company.
6. People who send you connection requests in spite of not knowing you, knowing you very briefly. It means that the person is highly insecure in his/present present position and is putting you down as a valuable contact who he will approach for a job or some matlabi reason in the future.
7. Anything emphasizing that they did something major in a short time. This means that they were quickly fired for not doing anything and they were expecting the firing and so did some bullshit to show activity in the short time they were around. Real achievers know nothing real and major happens in a short time.
On the flip side here are certain things that I see which add to the credibility of the person:-
1. Recommendations from other individuals whose enjoy credibility in the marketplace and who would not recommend lightly.
2. A LinkedIN paid user - this means the person is serious about using LinkedIN as a business tool.
3. A very brief outline for technical staff. This means the techie is right about not needing to put himself up on LinkedIN. It is more a resource for business development people.
4. A person who has made sense through their postings on LinkedIN groups as opposed to one who is just commenting to get noticed.
5. A person who is from an A-grade university and has mentioned societies he was part of during university days, is part of specific alumni groups - Harvard Grads of 2000 for instance. These groups are usually moderated and so very difficult for a poser to join.
Hope this was useful and welcome any comments. Sorry If I sound a bit harsh and judgmental but for me hiring the right team is one of the most important aspects of building a great company and these are things I wish I had known earlier.