Please see the TrademarkGuidelines page for a more general discussion of these issues.
This page was taken almost verbatim from the [Mozilla Trademark Policy FAQ].
What's the purpose of this document?
This document sets out to answer the common questions which arise about the use of the OSGeo Trademarks and Logos. Our code is free, but we do strictly enforce our trademark rights; we must, in order to keep them valid. This means that, while you have considerable freedom to redistribute and modify our software, there are tight restrictions on your ability to use the OSGeo name and logos, even when built into binaries that we provide.
What are the OSGeo Trademarks and Logos?
The OSGeo trademarks include, among others, the names The Open Source Geospatial Foundation, OSGeo®, OSGeo.org®, and the compass logo.
[the (r) symbols should be removed from OSGeo and OSGeo.org unless OSGeo registers these trademarks with the United States Patent & Trademark Office - jennifer daehler]
Thanks for your support -- of course you may. We will provide button icons for exactly this [link forthcoming].
Can I make a t-shirt/desktop wallpaper/baseball cap with the logo on?
Sure, if it's just for you, or if it's for others and no money or other consideration changes hands -- but note you are specifically precluded from producing items with the OSGeo name or logo for distribution at tradeshows, local user group meetings, etc. OSGeo operates the OSGeo Store [link] which sells a wide range of branded merchandise for exactly this purpose, with the proceeds going to support the Foundation.
Can I modify your logos and distribute the result?
No, sorry. To maintain our legal standing with respect to our trademarks and to prevent confusion or misunderstanding within the marketplace, you may not modify the logos in any way. Please see our branding and usage manual [forthcoming link] for the logo variations we currently provide.
You didn't answer my question.
Sorry, we're new at this too. Please contact us at [address] and we'll try to help you out.