Strange icon during boot. See photo.

The photo you attached cannot be seen correctly

Photo shows up fine here... And I can honestly say, that I've never seen such a strange artifact...

The photo showed up on my iPad. Hopefully this will help. I have no Idea what it might be.

Edit

Oh great, my photo didn't show up either.

Oh that's strange... I can't correctly see any photos attached in this post with my macbook

The missing photos are a reoccurring glitch since the Forum format changeover. I'll try again, hopefully somebody will see it and know what it is.

Oh nice I can finally see the photo. Thanks bobseufert🙂

You're welcome. Good luck sleuthing, I haven't a clue.

Try booting into the Safe Mode using your normal account to see if you get the same thing. Disconnect all peripherals except those needed for the test. Shut down the computer and then power it back up after waiting 10 seconds. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. When you reboot normally, the initial reboot may be slower than normal. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart by using the application un-installer. For each disable/delete, you will need to restart if you don't do them all at once.

Safe Mode - Mavericks

Safe Mode - About

Mine does it too. No idea what it is.

I think it had to do with MacKeeper - I've uninstalled it and its now gone

Mystery solved, thanks for posting the solution.