The readme should state the name and contact information of the author, as well as the conditions under which it can be used. Absence of a readme file indicates that the font has been tampered with, in which case you should not assume that it is a shareware font. However, the absence of a notice does not signify that the work is public domain, nor is such a notice required by law to retain ownership. If someone passes the fonts along without the documentation, trouble begins. Even if you get a font through a newsgroup posting, it does not automatically mean it is shareware either.
People make mistakes.
The anonymity of typeface origins and their designers is an unfortunate situation that has become increasingly detrimental to the field of typeface design. Before the democratization of type, which resulted from the introduction of personal computer technology, just over a decade ago, there existed an established collection of typefaces that were familiar to graphic designers typesetters, and others who worked with type. The introduction of new typefaces was a slow process that allowed ample time for the type community to become accustomed to the new designs. Because everyone in the industry could identify typefaces, graphic designers and typesetters had grown accustomed to leaving out credits for the typeface names or typeface designers, although they did credit their own work as well as that of photographers, printers and others whose work was included in the design piece. Today, typefaces are being introduced into the marketplace faster than any one can keep up with the selection.