I have been meaning to make this for some time. A chronological composite of David Bowie signatures from the mid 70's on to 2015. It is not as complete or neat as I'd like (not enough of earlier material for one) and I will add more observations regarding the signatures, but they are genuine and it does manage to show the evolution from C. 1976 on through the decades. There are scans and photographs of signed albums, album pages, playbills, IP, business cards, inserts, lithographs, books, scraps, photos, cards and a guitar. Various markers, pens and pencil. There are "open" and "closed" B' examples and some bits of handwriting also. I hope it is useful to you. The forgeries out there are largely of very poor quality, and usually fail from a lack of understanding regarding angle, basic construction and form. These examples are almost all dated. My favorites, oddly, are the 1983, 1993, 2003 and 2013 examples. The first 1993 example (with "open B") is in my collection and I like it because it appears a bit of a throwback in form and with that "o", and the bottom of the "B" looks like an axe blade. Comments and additions welcome. Click to see full image.
As we have the 1976 above, experimental in form IMO, here is a rare 77 signature for comparison. The image is from The 1980 Floor Show. By the mid 80's he would be using the fully simplified looped style that continued on through the 90's. The exemplar below has the letters mostly connected - this would be seen about half the time and perhaps a bit less 1978-80 or so as shown below in select examples. 1980 marks a year of great variation. By the mid 80's, and especially the 90's and beyond, the letters in "Bowie" were most always connected. Sometimes though, and early on, but clearly not always as the 1973 shows (hints of the simplified loop to come show here strongly), it is a skip, sometimes a jump - the "'10" below is actually connected again. Beneath that is the far more typical commonly seen simplified looped 1990's Bowie autograph which makes up the vast majority of his signatures - click for the full images: