warchalking
/ˈwɔːˌtʃɔːkɪŋ/noun
mass noun
- the practice of marking a series of symbols on walls and pavements to indicate the presence of a nearby wireless networking station that can be used to obtain illicit free access to the Internet黑客上网标记（在墙上或人行道上作记号, 指示附近有无线联网网站可用以免费非法闯入因特网）。
词源
early 21st cent.: from the use of chalk marks by tramps to indicate which homes were friendly and which to avoid.