<s>
The	O
rise	O
to	O
prominence	O
of	O
Twitter	B-Application
from	O
its	O
launch	O
in	O
2006	O
gave	O
rise	O
to	O
using	O
the	O
at	O
sign	O
("@"	O
)	O
as	O
a	O
description	O
for	O
directing	O
a	O
public	O
post	O
to	O
a	O
particular	O
user	O
,	O
especially	O
for	O
the	O
purpose	O
of	O
replying	O
to	O
another	O
user	O
's	O
post	O
(	O
i.e.	O
,	O
"	O
@janedoe	O
"	O
)	O
.	O
</s>
<s>
Only	O
after	O
the	O
usage	O
of	O
@	O
as	O
a	O
visual	O
means	O
of	O
directing	O
posts	O
to	O
specific	O
users	O
gained	O
currency	O
among	O
Twitter	B-Application
users	O
did	O
Twitter	B-Application
developers	O
begin	O
to	O
integrate	O
the	O
@	O
sign	O
as	O
a	O
fundamental	O
conversational	O
tool	O
on	O
the	O
site	O
.	O
</s>
<s>
Initially	O
,	O
@	O
was	O
used	O
by	O
Twitter	B-Application
users	O
occasionally	O
as	O
shorthand	O
for	O
other	O
words	O
,	O
such	O
as	O
location	O
or	O
time	O
.	O
</s>
<s>
The	O
first	O
to	O
propose	O
a	O
general	O
syntax	O
for	O
directly	O
addressing	O
users	O
in	O
posts	O
were	O
Ben	O
Darlow	O
and	O
Neil	O
Crosby	O
,	O
and	O
by	O
January	O
2007	O
,	O
more	O
Twitter	B-Application
users	O
began	O
to	O
take	O
notice	O
of	O
the	O
practice	O
with	O
various	O
degrees	O
of	O
acceptance	O
;	O
within	O
the	O
year	O
,	O
the	O
convention	O
trended	O
toward	O
combining	O
the	O
@	O
and	O
a	O
Twitter	B-Application
username	O
(	O
as	O
opposed	O
to	O
a	O
real	O
name	O
)	O
and	O
prepending	O
the	O
combination	O
to	O
the	O
beginning	O
of	O
a	O
post	O
in	O
order	O
to	O
indicate	O
a	O
reply	O
.	O
</s>
<s>
Twitter	B-Application
added	O
support	O
for	O
"	O
@replies	O
"	O
beginning	O
in	O
May	O
2008	O
,	O
with	O
any	O
combination	O
of	O
@	O
with	O
a	O
username	O
being	O
turned	O
into	O
a	O
hyperlink	O
to	O
the	O
profile	O
.	O
</s>
<s>
On	O
March	O
30	O
,	O
2009	O
,	O
Twitter	B-Application
updated	O
the	O
feature	O
and	O
renamed	O
it	O
"	O
Mentions	O
"	O
(	O
i.e.	O
,	O
to	O
"	O
mention	O
"	O
user	O
"	O
@janedoe	O
"	O
)	O
so	O
as	O
to	O
include	O
non-reply	O
posts	O
directed	O
at	O
individual	O
users	O
.	O
</s>
<s>
Beginning	O
September	O
2009	O
,	O
Facebook	B-Application
integrated	O
the	O
at	O
sign	O
as	O
a	O
mentioning	O
feature	O
;	O
typing	O
"	O
@	O
"	O
in	O
a	O
post	O
automatically	O
initiates	O
a	O
drop-down	O
autocomplete	O
list	O
containing	O
names	O
of	O
"	O
friends	O
"	O
,	O
groups	O
and	O
pages	O
,	O
which	O
,	O
after	O
one	O
being	O
selected	O
and	O
the	O
post	O
published	O
,	O
links	O
to	O
the	O
profile	O
,	O
group	O
or	O
page	O
.	O
</s>
<s>
The	O
plus	O
sign	O
("+"	O
)	O
was	O
utilized	O
on	O
Google+	B-Application
to	O
select	O
a	O
user	O
or	O
page	O
.	O
</s>
