Determine minimum OSX version a binary was compiled for

Use otool -l /path/to/binary and inspect the LC_VERSION_MIN_MACOSX load command; specifically, the version field.

For example, a binary compiled with the 10.8 SDK with deployment target (-mmacosx-version-min) 10.8 should have an LC_VERSION_MIN_MACOSX like this:

Load command 9
      cmd LC_VERSION_MIN_MACOSX
  cmdsize 16
  version 10.8
      sdk 10.8

whereas a binary compiled with the 10.8 SDK with deployment target 10.7 should have an LC_VERSION_MIN_MACOSX load command like this:

Load command 9
      cmd LC_VERSION_MIN_MACOSX
  cmdsize 16
  version 10.7
      sdk 10.8

An alternative to using otool | grep is to use vtool (available on macOS 10.15 and later).

For example:

❯ vtool -show-build ./test
test (architecture x86_64):
Load command 10
      cmd LC_BUILD_VERSION
  cmdsize 32
 platform MACOS
    minos 12.0
      sdk 12.3
   ntools 1
     tool LD
  version 764.0
test (architecture arm64):
Load command 10
      cmd LC_BUILD_VERSION
  cmdsize 32
 platform MACOS
    minos 12.0
      sdk 12.3
   ntools 1
     tool LD
  version 764.0

As noted in the comments, this does not work on static libraries or object files. From man vtool:

     Currently vtool only operates on final linked binaries, such as executable files, dynamic libraries, and bundles. Because the
     executable code in Mach-O final linked binaries cannot be moved or resized, and because the load commands reside between the mach
     header and the executable code, there is only a limited amount of space available for vtool to save changes. Set operations that
     add or resize load commands may fail if there isn't enough space in the Mach-O file availble to hold the new load commands.

vtool does, however, let you edit the build and source versions in the mach header, provided there is enough space for your revisions.

The load command that is mentioned in the accepted answer is not listed when I build a modern macOS executable. However LC_BUILD_VERSION does contain the minos and sdk fields:

Load command 10
      cmd LC_BUILD_VERSION
  cmdsize 32
 platform 1
    minos 11.0
      sdk 11.1
   ntools 1
     tool 3
  version 609.8