I have seen a few models of the Skyrim quest markers but couldn't find a Fallout version, so I just made one (while at work, don't tell my boss). 

Can print in whatever color, but green pla makes the most sense to me. Can be attached wherever with some double sided tape. Makes for great nerding out if you are into that sort of thing. The one connector piece between the main body and the top square may be somewhat fragile depending on your print settings, but I don't think it will be a huge issue unless you are throwing it at your friend (assuming you have at least one of those). 

Could be printed in green for that extra radiation-y feel