The magic file on most UNIX-like systems today should have the necessary information to identify RPM files. But in case your system doesn't, the following information can be added to the file:
#-------------------------------------------------------------------
#
# RPM: file(1) magic for Red Hat Packages
#
0 beshort 0xedab
>2 beshort 0xeedb RPM
>>4 byte x v%d
>>6 beshort 0 bin
>>6 beshort 1 src
>>8 beshort 1 i386
>>8 beshort 2 Alpha
>>8 beshort 3 Sparc
>>8 beshort 4 MIPS
>>8 beshort 5 PowerPC
>>8 beshort 6 68000
>>8 beshort 7 SGI
>>10 string x %s
|
The output of the file command is succinct:
# file baz
baz: RPM v3 bin i386 vlock-1.0-2
#
|
In this case, the file called baz is a version 3 format RPM file containing release 2 of version 1.0 of the vlock package, which has been built for the Intel x86 architecture.