Currently by colour for my machines, for the most part, with the IP address running alphabetically:
a5000 = Acorn A5000 (it's cream so would clash with clearbox) = .101
bluebox = Indigo2 (which may become tealbox if I set up the Octane permanently) = .102
clearbox = Pi in a clear acrylic case = .103
486elvis = PC-on-a-Eurocard inside the A5000 ("elvis" was the maker's codename for the board) = .104
epc = EspressoPC (should be "silverbox" but "epc" is shorter!) = .105
greybox = Acorn RiscPC = .107
pccard = 486DX co-processor in the RiscPC (whose NIC has a virtual second interface with IP .116)
redbox = Fuel = .118
whitepi = Pi2 in a white case = .123
Others have "unconventional" names (e.g. wife's laptop is "mine", i.e. hers rather than ours
, entirely prosaic names ("lenovo" for my work laptop) or ones driven by finding a suitable gap in the alpahbetic IP scheme (e.g. "xarm" and .124 for the cream A540 that runs RISCiX, as "a" and "c" were already allocated).
When I mostly had Acorns the scheme was model number (a5000, r140, a540, riscpc) for the name and year of manufacture (19xx) for the IP address (93, 89, 91 and 94, then 95 for a Compaq Deskpro XL5/133 whose name I forget).