For instance:
rs<-c("copyright @ The Society of mo","I want you to meet me @ the coffeshop")
s<-gsub("@.*","",rs)
s
[1] "copyright " "I want you to meet me "
Or, if you want to keep the @ character:
s<-gsub("(@).*","\\1",rs)
s
[1] "copyright @" "I want you to meet me @"
EDIT: If what you want is to remove everything from the last @ on you just have to follow this previous example with the appropriate regex. Example:
rs<-c("copyright @ The Society of mo located @ my house","I want you to meet me @ the coffeshop")
s<-gsub("(.*)@.*","\\1",rs)
s
[1] "copyright @ The Society of mo located " "I want you to meet me "
Given the matching we are looking for, both sub and gsub will give you the same answer.