The thing with the red dot on it is the Cartridge Drop Lever.
"The end of the cartridge drop lever protrudes from the right side of the receiver, above the trigger, and is marked with a red dot. When the dot is visible, the hammer is cocked and the weapon is ready to fire.
The red dot on the cartridge drop lever, when visible, indicates the carrier is “free†and the magazine can be loaded.
If the cartridge drop lever is depressed before loading, the carrier loses its “free†status.
To free the carrier on a cocked weapon, simply depress the carrier latch button and load normally.
On an un-cocked weapon, pull the bolt to the rear and release it, cocking the weapon.
When depressed, the cartridge drop lever releases a shell from the magazine on a loaded weapon.
On an unloaded weapon, the cartridge drop lever has to be depressed to lock the bolt to the rear."
(Quoted from page 13 of an Adobe PDF file I found out there on the web, which is a scanned copy of an HK Benelli Shotgun Training manual.)
Here's a link to Benelli Italy's FTP site, where you can download User's and Spart Parts Manuals:
Benelli Italy M3 manuals
EDITED TO ADD: If you have Windows XP's built-in Internet Connection Firewall enabled on your NIC, the FTP data connection may not be able to initiate back to your machine. I had to temporarily disable the firewall on my machine to get the FTP directory listing and file transfer functions to work in my browser.
