sign on vs contract out

sign on and contract out both are verbs.

Word	Noun	Adjective	Verb	Adverb
sign on	No	No	Yes	No
contract out	No	No	Yes	No

As verbs, contract out is a hyponym of sign on; that is, contract out is a word with a more specific, narrower meaning than sign on:

sign on (verb)	contract out (verb)
engage by written agreement	refuse to pay a levy to a union for political use
	assign a job to someone outside one's own business