Noun: Benchpressing [fest].
Penkkarit (or more formally, penkinpainajaiset) is an event celebrated by Finnish upper secondary school students in the spring of their final year on the final day of school before the start of matriculation exams. Traditionally, penkkarit is a Thursday in late or mid-February. (In 2014, it is Thursday, February 13th.)
Penkki means ”bench.” Penkinpainajaiset translates loosely as ”bench pressing.”
In the example photo, the phrase ”Penkkarikyltit ovat yli arvostettuja” means ”Penkkarit signs are overrated.”
Read more about penkkarit here.