I read your question and found it interesting, in as much as you want your title or position to be known however you also don't want this to sound pushy or impolite. Firstly, you did not explain if you have created a letter head for yourself , something simple with your name and title on the top. As there isn't an indication of your group, lets call it the Neighbourhood Tree Committee, hence
Neighbourhood Tree Committee
122 Elm Street, Watersburg, State, code phone
Danny Wood, President
Dear so and so,
The other alternative is to simply put your logo or title etc, under your name at the bottom of your salutation..
The salutation itself in all etiquette should remain either Sincerely yours or Yours truly, otherwise you run the risk of appearing somewhat brazen in your correspondence. Polite as you noted is of essential in business correspondence or obtaining loyalty and respect with your correspondence. The writer, (answerer) has been president and vice president of several groups and charities, hence my view, as its important to get ones attention yet remain cordial and not to up man ship (so to say).. good luck with your endeavours and am certain you will do well here.