Good markers for ensuring accurate alignment?

Is there a set of shapes or markers that you have found to work well for a static camera array? I’m looking to ensure that all of my cameras align properly. Thanks in advance for any suggestions.

A stand covered with a sheet of a newspaper works very well for me…

HI Neil Nafus

for what sort of subjects need use the markers ?
we plan to add RAD coded targets support…

Oh, I don’t have anything in mind in particular. I’m just trying to optimize my setup to ensure optimal alignment and I was curious what would be most recommended.