If you use the Terminal on OSX will often see an @ after the standard permissions when you do an “ls -l”, like this:

drwxr-xr-x   8 tonyarkles  staff        272  9 Dec 09:29 search benchmark
-rw-r--r--   1 tonyarkles  staff       3745 24 Nov 15:35 sprite.png
-rw-r--r--@  1 tonyarkles  staff  728221696 15 Jan 22:03 ubuntu-8.04.1-desktop-i386.iso

The presence of the @ indicates that there are extended attributes. You can use the command xattr to have a look at them:

Tue Jan 20 10:05:25: ~/Desktop$ xattr ubuntu-8.04.1-desktop-i386.iso 
com.apple.quarantine
com.vmware.backupReenabled

I’m not particularly sure what the vmware attribute is all about, but the com.apple.quarantine attribute is what marks a file as coming from an untrusted source. If you want to look at the value of the attribute, you can use the -p option:

Tue Jan 20 10:07:37: ~/Desktop$ xattr -p com.apple.quarantine ubuntu-8.04.1-desktop-i386.iso 
0000;496ff4c5;Firefox;|org.mozilla.firefox

And if you want to drop it, you can use the -d option.

Tue Jan 20 10:07:46: ~/Desktop$ xattr -d com.apple.quarantine ubuntu-8.04.1-desktop-i386.iso 
Tue Jan 20 10:09:12: ~/Desktop$ xattr ubuntu-8.04.1-desktop-i386.iso 
com.vmware.backupReenabled