Abbreviations could be with the pronounciationpronunciation of the word, for example, 'n' for 'and', and 'k' for 'okay'. Other such abbreviations can be seen here..
It really depends where you are. If you are texting, then may bemaybe 'N', if you are putting it as a message, probably either, if you are putting it as the name of something, probably 'K'.