motion vs sign

motion and sign both are nouns.

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

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

motion: the use of movements (especially of the hands) to communicate familiar or prearranged signals
sign: a gesture that is part of a sign language

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

motion: show, express or direct through movement
sign: make the sign of the cross over someone in order to call on God for protection; consecrate

motion (noun)	sign (noun)
a change of position that does not entail a change of location	structure displaying a board on which advertisements can be posted
the act of changing location from one place to another	a public display of a message
the use of movements (especially of the hands) to communicate familiar or prearranged signals	a gesture that is part of a sign language
a formal proposal for action made to a deliberative assembly for discussion and vote	any nonverbal action or gesture that encodes a message
a natural event that involves a change in the position or location of something	a character indicating a relation between quantities
an optical illusion of motion produced by viewing a rapid succession of still pictures of a moving object	a perceptible indication of something not immediately apparent (as a visible clue that something has happened)
a state of change	a fundamental linguistic unit linking a signifier to that which is signified
	an event that is experienced as indicating important things to come
	(astrology) one of 12 equal areas into which the zodiac is divided
	having an indicated pole (as the distinction between positive and negative electric charges)
	(medicine) any objective evidence of the presence of a disorder or disease

motion (adjective)	sign (adjective)
	used of the language of the deaf

motion (verb)	sign (verb)
show, express or direct through movement	be engaged by a written agreement
	communicate silently and non-verbally by signals or signs
	mark with one's signature; write one's name (on)
	make the sign of the cross over someone in order to call on God for protection; consecrate
	communicate in sign language
	place signs, as along a road
	approve and express assent, responsibility, or obligation
	engage by written agreement