The only way that you will know for sure is by taking it to a professional autograph clarifier (for want of a better word), often these people are former forensic experts for the police and have delt with bank forgeries and the like. Taking your autograph to them will be costly, but will give you piece of mind. However, for practicle reasons I suppose you could match your signature to a reputable dealers copy, if they are alike then odds are they are real.
Chin up though... odds are that of the hundred + signatures that you have collected maybe a small handful are secretarial.
Don't give up collecting on the off chance that a small amount of your collection MAY (element of doubt) be secretarial.

All the very best in your collecting... long may it continue.

YOURS_SINCERELY

Do you have fun recieving a autograph in the mail? Does it cheer you up? Chances are all your autos are real. Getting into this hobby you take the chance of recieving fakes or having someone else sign it. For all we know everybodys autograph on this site is not from the real person because we werent there to see it signed. But as long as your happy thats all that matters. hope this helps

i've been collectin autographs for a year and a half, and now im startin to think that all the 132 auto's i got aint real and feel as though that its been a waste of time in collectin, as ppl tell me that its always secretaries or agents that have been hired to sign people's fanmail, and we receive fake auto's instead of real and now im ready to stop collectin auto, as i want to know im receivin real auto's from cameron diaz or angelina jolie, and want some1 to clarrify me on how to deal with this prop.

thank u