Looking through the pics of both species it seemed to me that on most dorsisignatana the forward dark patch is more compact while on most similana that patch is more likely to be stretched out some, or that's the impression I got anyway. But I agree that the two species are easily confused and I suspect that there could be disagreement over many of the images sitting in both species pages. But I'll move it to genus level since there is disagreement on this one.

... (or more confusing) I am not disagreeing and after hearing your explanation, I think you might be right. I should point out that Jason Dombroskie has an example at MPG where forward dark patch merges with the neighboring patch but perhaps it is misfiled.

Mark Dreiling's submission here has a link to the BIN shown here: BOLD:AAB3378

It appears that he actually has three specimens there and I took a look at the barcode tree PDF under "TREE RECONSTRUCTION OF BIN & NEAREST NEIGHBOR:" which shows two specimens labeled as dorsisignatana nested between his examples. I'm not sure how to interpret this. The next closest BIN is BOLD:AAB337 which has only dorsisignatana in it.

and that tree reconstruction diagram with the two dorsisignatana stuck in there confuses me even more so I can't say what that's all about. But there is obviously a lot of variation within each of those two species and like you said earlier, it's probably not possible to be completely certain which is which just from photographs. I probably should have just settled for genus when I posted this moth in the first place. It's frustrating to not be able to take all the way to species and I do try to be as certain as possible before going there but I'm bound to be wrong sometimes. I have this one labeled as E. similiana in my own records and I think I'll leave it at that, but will leave it at genus here on BugGuide since I can't really say for sure.
Thanks for your thoughts.