1. This is the equivalent of 'pig' in English - NOT the animal, but when the word is used to rudely address a policeman
2. It is pure slang, not to be used in any formal context - Popular in Turkish translations of Hollywood flicks
3. The literal meaning of the word is 'mirrorless', 'without a mirror', 'lacking a mirror'

Whilst not very polite, this is a funny and cute slang expression. The word ayna means mirror, and aynasız means mirrorless. This word tells us that the Turkish society believes cops are people who do all sorts of immoral things themselves, but catch 'ordinary' people who do the same, and based on that, they don't have a mirror to see their own 'ugly faces'. Cool or what? :-)