My first reaction is that this is simply an attempt to write what is said when it is said quickly. Logically you would write the apostrophe either side of ‘n’ to indicate that the ‘a’ and the ‘d’ are missing and the space either side would be appropriate for the missing letters, too. That said, it’s probably best to write the full word ‘and’. It’s not asking a lot, is it? No doubt chip and pin will receive the same treatment.
It would probably be better to use ‘and’ in anything professional. I believe the ‘n’ would be more slang than anything. When we say fish and chips for example, we tend to swallow the ‘and’ and it sounds more like the letter ‘n’.