How can I tell without just sitting up there and trying to remember which hens are laying and which aren't? Or is that the only way?
Use a "Catch Nest Box". Someone can chime in with another name for them to help you out hopefully. A next box that let the hen in when she lays but cannot exit until you let her out. You can track you laying hens this way. People do sell them but I don't remember off the top of my head. Hope this helps.