sign-language vs signed

sign-language and signed both are adjectives.

Word	Noun	Adjective	Verb	Adverb
sign-language	No	Yes	No	No
signed	No	Yes	No	No

As adjectives, sign-language and signed are synonyms defined as:

Other synonyms of sign-language include gestural, sign.

sign-language (adjective)	signed (adjective)
used of the language of the deaf	having a handwritten signature
	used of the language of the deaf