Depends on whether that symbol appears in whatever font has been assigned to
the message box (right-click on your desktop, select Properties, go to the
Appearance tab and click on the Advanced button in the bottom right) If so,
and you know what the Ascii code is, you can use something like:
Msgbox "Press " & Chr(nnn)
(where nnn is whatever the Ascii code is for right triangle)
For instance,
Msgbox "This message " & Chr(169) & " 2008"
displays a message box with the copyright symbol on it on my machine.