What characters are on this ceramic jar?
It should be 福壽康寧 (fú shòu kāng níng; simplified: 福寿康宁).


福
康
壽
寧


I'm pretty certain about the first 3; 寧 is the only one that is hard to tell, but based on context, it should be 寧.

EDIT: And this is what it means: good fortune, long life, health and peace