Here's a quick sample, showing the current empty 'diamond' shape:
symbol1 v=diamond h=7pct c=red;
proc gplot data=sashelp.class;
plot height*weight=1;
run;
I believe several filled markers, which you can specify directly on the symbol statement's "value=" are being added in v9.3, such that you could specify
something like ...
symbol1 v=diamondfilled h=7pct c=red;
But, in the meantime, you can specify any font character that you might have
access to (especially in v9.2 sas, which also supports unicode characters).
Here is an example, using a solid diamond from the Windows Wingdings font,
(character '75'-hex) for example.
symbol1 font="wingdings" v='75'x h=7pct c=red;
proc gplot data=sashelp.class;
plot height*weight=1;
run;