Moxie was assigned an official ELF machine number this week! You can check it out here: http://www.sco.com/developers/gabi/latest/ch4.eheader.html.
All ELF files start with a header describing properties of the object at hand. One of the most important properties is the 'machine' type. The machine type identifies the basic architecture for which the given binary is relevant. It is represented as a 16-bit integer, so, for instance, MIPS is 3, ARM is 40, AVR32 is 185, and now, I'm happy to say, Moxie is 223.
Linkers, loaders, and similar tools examine the machine number to make sure they're working with the right kinds of files. This saves us from linking SH4 and Sparc objects into x86_64 executables.
Until recently the Moxie GNU binutils port had been using a temporary machine number of 0xFEED. Every new architecture, however, should get an official number assigned by the System V gABI maintainers. Just send a nice email requesting the number assignment to firstname.lastname@example.org and they'll increment their most recent number and add you to the list.
If you look at GNU binutils you'll see that many ports, including Moxie, live for quite some time using arbitrary machine number values unlikely to conflict with the slowly incrementing official numbers. Others, like the FTDI FT32 port, get their numbers (222) assigned in advance of port submission. If you go the same route I did, you'll see that binutils has a mechanism whereby you can identify the main machine number (223) as well as alternative numbers (0xFEED) to ease in the transition. This is all that needed doing: https://sourceware.org/ml/binutils/2015-01/msg00105.html.