The way I read it, what they are asking you to do is to sign a document stating that all the music is your original stuff, hence no royalties are due to anyone for anything you play. That gets them off the hook for any outfit that might make a royalty claim based on some band(s) at the event performing music for which the copyright is owned by an artist they represent.
If my analysis is correct, then if you play covers you are not telling the truth if you sign the form.
I've never heard of either of these organizations. Info about the IPRS is found at:
http://www.iprs.org/aboutus.asp / Their website says they are in India and exist to collect royalties: "Well, in short, the business of IPRS is to issue Licences to users of music and collect Royalties from them, for and on behalf of its Members i.e. the Authors, the Composers and the Publishers of Music and distribute this Royalty amongst them after deducting its administrative costs."
This smells. My read is that they created a way to generate money and skim a cut off the top.
I don't know if either organization has any legal standing in the US. BMI and ASCAP are the only organizations I know of that have legal standing here - but I'm not a lawyer, so I may not be interpreting this correctly.
PPL is based in London:
http://www.ppluk.com/ . I don't know whether they have legal standing in the US either.
Edit: I just realized you re in India. Find out the status of these groups in YOUR country.
I am very interested in seeing what others have to say. It seems to me that you don't have anything to lose by signing a disclaimer, but do NOT sign a release that gives the event permission to record your performance and re-sell it.