A sign is a mark or shape that always has a particular meaning, for example, in mathematics or music. 符号
adjective [原级] 有符号的；已签字的；有正负之分的
The treaty was signed on 24 March. 条约是3月24日签订的。
verb [vt. 及物动词] 署名；写下；预示；示意（sign 的过去分词）
You haven't signed the letter. 这封信您还没有署名。
