Depends on what you mean by “post.” Are you talking about any individual page? Then you’d probably want {{.IsPage}}.
Otherwise, if you keep your posts in a directory (ie, contente/posts), this will work:
{{if eq .Section "posts"}}
YOUR STUFF HERE
{{end}}
You can also range through them…
{{range where .Site.Pages "Section" "==" "posts"}}
{{end}}