The IPC stands for the International Proficiency Certificate.
It was created by US Sailing organization and subsequently copied by ASA. It is meant to be a substitute for an international license.
If you hold an IPC you will probably get by with it in the Mediterranean BUT make sure that your resume is very strong. Yacht charter companies know that the IPC can be issued with as little as a few days of sailing training and no real experience. YET the yacht charter company will turn you down if you do not have a worthy resume. Think about it from an insurance company point of view if a boat is crashed the insurance company first looks at the claim and who was the skipper that the charter company gave the boat to. If the resume is too light the insurance company will not pay out on the claim. Thus charter companies check resumes as well as the sailing license.
Ultimately, at NauticEd, we are biased toward the SLC that we administer because of the standards we adhere to. The SLC is only awarded to those who have sufficient experience to automatically qualify to charter. When the NauticEd student's resume is charter worthy and the student meets the proper legal conditions only then does our software issue the SLC license. Thus SLC holders are guaranteed to be accepted for charter - no surprises (like "oh you need to hire a captain for a week") on the dock in Croatia.
When you book a yacht charter with NauticEd Sailing Vacations, we run a check on your resume and license and we preclear you with the yacht charter company.
See www.nauticed.org/SLC for the detail on the SLC
See http://www.nauticed.org/sailing-blog/how-to-gain-your-slc-mediterranean-sailing-license/ on how to get the SLC
If you are a competent sailor but undocumented, you will have no trouble gaining the SLC. Basically you do online lessons and a one day assessment of your skills and knowledge on the water. You will not be subjected to a multi-day training that is required for the IPC.