sign

noun:a visible indicator or symbol that conveys information, instruction, or warning
- The stop sign at the intersection reminded drivers to halt.
noun:a mark or gesture made with the hand, body, or other means to communicate a message
- She gave a quick thumb‑up as a sign that everything was okay.
noun:an event or circumstance that suggests something may happen
- Dark clouds on the horizon were a sign that a storm was approaching.
verb:to indicate agreement, support, or endorsement by affixing a signature or mark
- Please sign the contract before submitting it to the office.