sign in vs check in

sign in and check in both are verbs.

Word	Noun	Adjective	Verb	Adverb
sign in	No	No	Yes	No
check in	No	No	Yes	No

As verbs, sign in and check in are synonyms defined as:

sign in and check in: announce one's arrival, e.g. at hotels or airports

sign in (verb)	check in (verb)
announce one's arrival, e.g. at hotels or airports	announce one's arrival, e.g. at hotels or airports