painter vs sign painter

painter and sign painter both are nouns.

Word	Noun	Adjective	Verb	Adverb
painter	Yes	No	No	No
sign painter	Yes	No	No	No

As nouns, sign painter is a hyponym of painter; that is, sign painter is a word with a more specific, narrower meaning than painter:

Other hyponyms of painter include finisher, house painter, letterer, scene painter, stippler.

painter (noun)	sign painter (noun)
large American feline resembling a lion	someone who paints signs and billboards etc.
a line that is attached to the bow of a boat and used for tying up (as when docking or towing)
an artist who paints
a worker who is employed to cover objects with paint