Pegao (pegado)-
2LF-
This is a classic example of a Spanish verb form pegado that's commonly pronounced as pegao. Therefore, if you look it up in the dictionary as pegao you will not find it unless it's a dictionary of slang terms. However, you will definitely see examples and the meaning of the verb pegar and its past participle pegado.
In brief, the loss of [d] in between vowels thus rendering the pronunciation "ao" of such verb forms (the pronunciation only) is very common in the Spanish speaking world today. It was once associated with informal and/ or uneducated speech but this is no longer the case. Commonly known as a salient feature of Caribbean Spanish but it is equally as common in many regions or countries in Latin America and Spain.
Some good quality Spanish text books may mention this phonetic aspect of Spanish. Specialized textbooks and some dialectology references will also mention this property of speech. In sociolinguistics studies you will see explanations that it crosses all class lines of speech. There are many verbs that are pronounced this way in daily dialogue. Once again songs titles, commercial ads/signs (as in your example) will evidence this verb form however, in formal Spanish, verbs (the past participle) with the ending -ado should not be replaced by -ao.
Expressions-
1/ As for expressions there is a common one 'que me quiten lo bailao' (from bailado) that you hear often in songs. There's one for you to look up.
2/ You will also hear bailar pegao or bien pegadito.
3/ Raspar pegao= If I am correct with the meaning of this expression, IMO it's quite liberal for a subway ad. Let's see if others give the meaning of it.
Once again 2LF you have made a good observation and I like the fact that you question the meaning of something that you don't understand. In Spanish or any language, you should not assume anything.
-LDG.