Set the global to be a checkbox field, with a value list. Check Current and Special Order and it should match both.
If you have FileMaker 11, use a portal filter instead of a filter in your relationship:
Products::Status = "Current" or Products::Status = "Special Order"
If you want the filter at the relationship level (had to do it that way before the release of Filemaker 11...) you can use this calculation field in place of your global field:
List ("Current" ; "Special Order")
(You can also just enter "Current", press return and then enter "Special Order" in the current global text field that you are using.)
This will match to all products recorsd with a status of "Current" or "Special Order".
You guys are the best!!!