What does this symbol mean?
It is 氏 as in 姓氏 (family name)

In ancient time, China was a 母系社会 (matriarchal society). People got their family name from their mother side. That was called '姓'. 

Eventually, 父系社会 (patriarchal societies) started to develop. People began to add the family name from their father side in addition to their 姓 (family name from the mother side) and that family name from the father side was called '氏'

For example: A woman's family name was 杜 and gave her son the name 明, this 明 person would have a 姓 of 杜 and his full name would be 杜明. 

However, his father's family name was 李, and this 明 person could legally call himself  '杜姓李氏' (杜 was his family name from his mother's side, and 李 was his family name from his father's side)

Eventually, matriarchal society societies was replaced by patriarchal societies completely. The term 姓氏 was consolidated to mean family name (from the father side)


In modern Chinese, the term '姓氏' refers to 'family name' and '姓' is the standard shortened form of '姓氏'


When you ask what is someone's family name, you only ask what is his 姓, never what is his 氏. The full term '姓氏' is rarely used colloquially. It appears mostly in written form.


氏 on its own refers to: 


A woman's maiden name. For example: 杜门李氏 (married to the 杜 family and maiden name was 李)
Clan's name (interchangeable with 姓) -  both '杜姓一族'  and '杜氏一族' means 'the clan of 杜'