How can I create a transparent marker/symbol in ArcGIS Desktop 10?
I am trying to do this by setting up the transparency of the layer, but the markers seem unaffected by this change.
The best way to import symbols in a map document is to use EMF format. This will maintain the vectors, allow resizing in ArcMap without loss of quality. Since there is no "background" to a vector drawing, it will appear correctly transparent in ArcMap.
Alternately, you can make the bitmap marker method work by filling the "transparent" background portions of your symbol with a key colour that does not appear elsewhere in your image be aware that using bitmap markers may adversely affect output quality.
You are going to the marker layer's properties Display tab and changing the transparency, correct? As I'm guessing you know this is the main way to change the transparency of any layer, including marker symbols. If that doesn't work, I wonder if you don't have have some kind of read-only problem. May be worth trying to copy that layer and paste it in as a new layer and try to change the transparency on the new copied layer.