How to position mileposts?

I have gotten to the point where I thought having just non interactive objects would affect the realism of my route. So I decided to create some mileposts.
The thing is that I have zero experience with mileposts and similar objects, and they keep vanishing as soon as I place them in the game (even the Kuju ones). What is the magic trick in order to get them to remain visible and usable in scenarios? I have searched the web to no avail.
When I use the select tool (the dotted line that drags along the top of a loft, visible in the upper left of the drop down menu), these don't appear. I am completely new to this, so please excuse the silly questions.
Edit: Also, are there any tutorials around the place that indicate how to get working speed limit signs in the program?
Thanks
The thing is that I have zero experience with mileposts and similar objects, and they keep vanishing as soon as I place them in the game (even the Kuju ones). What is the magic trick in order to get them to remain visible and usable in scenarios? I have searched the web to no avail.
When I use the select tool (the dotted line that drags along the top of a loft, visible in the upper left of the drop down menu), these don't appear. I am completely new to this, so please excuse the silly questions.
Edit: Also, are there any tutorials around the place that indicate how to get working speed limit signs in the program?
Thanks