One way, is to run "reg" first, and then using "outreg" with option starlev(10, 5, 1) to output the results. YOu may need to install outreg ado file (try "search outreg" first and then install).
if you use outreg2, after running reg, using "outreg2 using regout, replace", I think the default is flagging the coefficients by .1 (*), .05 (**) and .01 (***) already. So in this case, if "***", means significant at all 3 levels, if "**" at .05 and .1, "*" for .1.