Alternator....

[Big Rig]

What are the first signs to look for if it is DEAD????

[98valk]

while the engine is running there should be minimum 14V~ at the battery at idle, raise rpms ALTERNATOR: OUTPUT: 546 WATTS & 14.2 VOLTS @ 3500 RPM

[Gabriel]

You did not state why you suspected the Alt.;
If you have a dead or sulfated battery you will probably not see the suggested voltage.
A battery in one of these conditions will draw enough current to keep the voltage low.
Unless you have an induction clamp or probe I would suggest you substitute a known good battery from your riding mower or car if the bike battery is low or dead, then check the voltage.
Just be sure to disconnect the bike battery completely

[Blackduck]

If by dead you mean you have checked it is not producing any voltage and now wish to know what to look for as a cause.
Brushes and then a continuity check on the rotor.
Mine died and there was a broken wire on the stator winding. Was very hard to find as the wire had basically cracked where it was wrapped around a post before going to the slip ring.

[Big Rig]

The reason I ask, just lost two batteries this year....first one, I thought maybe the kids turned the key on ( I leave it in the bike). So I replaced it two weeks ago, went for a ride and parked it. Went out to start the bike to do an oil change and nodda...

This time, the key was not in the bike. No other power draw while the bike is garaged.

99 IS...never had any other problems.

[gordonv]

As stated, take a volt meter to the battery while the bike is running. At 1500 + it should be producing over 13.5 V.

If you only have battery voltage (check it before you start the bike), then no power is reaching the battery.

This can be 1 of any multiple of problems.

[Savago]

It may also be some accessories/wiring draining the battery. Do you leave the bike in a trickle charger?

[da prez]

  I will get on my soap box again. S T A R T  from the basics. Remove and clean the battery terminals. Remove and clean all the battery connections and grounds . Unbolt the frame and engine grounds. Clean all , dia-electric compound (some will disagree ) the connections . Charge the battery on the bench while you are doing the cleaning of connections. It will take you about an hour to do. It is better than pushing the bike home. I have done this on more bikes than I care to count. I work part time at a shop and also have my own shop. We have sold batteries and explained about connections only to have them come in or tow in bikes with bad batteries we sold. I take them into the shop and show the procedure for installation. This way they see that the battery is good and I get paid for them not listening. 

                                       da prez