Jennyfurwhen,
You've found what has proven an enduring mystery to banjo uke enthusiasts; no one knows definitively, at least no one posting on the internet, who made this particular uke. This company made a variety of no-names of varying degrees of ornate-ness. Most have no decoration at all, and just follow this basic pattern with plain maple, but this one here is their most ornate model, and I've run across a few over the years.
Yes, headstocks DO tend to constitute a signature, but this particular company used a few different headstocks, sometimes varying the headstock for different jobs. They made ukes for Sears, Progressive Musical Instrument Company of New York (P'Amico), La Pacific, Neptune, B&J NY - the 'Mele' and a cheaper model, and several others; most had a spatulate headstock. This one has a spatulate headstock with those extra indentations in the waist. I've also seen the same ornate uke but with a typical "Harmony" or "Martin"-style three-pointed headstock. it's slightly bewildering.
The sheer numbers of them out there - and several hundred come up for sale on eBay every year - make me think that the company is, in fact, Harmony of Chicago, which made several hundred thousand instruments each year in the 20's, many of them ukuleles, and a staggering high production of 300,000 instruments in 1930 - at the height of the depression. A few have been found with Harmony's "Standard Approved" stickers on the back of the headstock, which is another point in favor of Harmony in my book.
All that said, this is not an expensive uke, probably in the $4-5 price range throughout the 20s and early 30s. They are also not high quality instruments, but if in good shape, should be a lot of fun to play. The inlays and decals increase the value significantly.
So, if you've read this far, I still haven't answered your question; what is it, exactly? If you think as I do that its a Harmony or not doesn't really matter; you'll find that the value is remarkably consistent on these. Unadorned, they run from $50 to $100 for instruments in good shape. Tricked out, like yours is, you'll find them going for between $80 and $180 based on condition and playability. $150 is a reasonable price if the instrument is a good player and you like the sound.
Let us know what you do - I love these things and I'm always looking for more information on them. Here are a few links that should give you some information.
http://www.musurgia.com/products.asp?ProductID=668&CartID=4828429102010
Antebellum has restored several of these and similar:
http://antebelluminstruments.blogspot.com/2009/07/c1920-neptune-banjo-ukulele.html
there's several on eBay now:
http://cgi.ebay.com/VINTAGE-BANJOLE...219?pt=LH_DefaultDomain_0&hash=item4cf32520d3
Scroll Down:
http://ukuleleguide.com/gallery.html
The banjo uke page is a great resource, and if you go to the auction records page for the names above, you can get a sense of what some have been going for.