calling card
noun [ C ] uk/ˈkɔː.lɪŋ ˌkɑːd/ us/ˈkɑː.lɪŋ ˌkɑːrd/
(PHONE)
US (also phone card)电话签账卡（使用者可以在任何地方使用电话，费用通过其家里电话账户支付）
a card that allows the user to make calls from anywhere and charge it to his or her home phone account
(VISIT)
（旧时在正式访问他人宅邸后留下的）名片
(in the past) a card with their name on it that a person left after they had made a formal visit to someone else's house, etc.
(OF PERSON)
名片式行为，标志
something that describes or shows a person's typical qualities
Slow romantic songs are his calling card. 缓慢的浪漫歌曲是他的标志。