Activity Streams are an extension to Atom feed format to add info about actor and verb to the feed, i.e. who-does-what. This makes it possible to just subscribe to certain activities of the originator or a feed, and filter just for the activities of interest.
To a certain extend an icon that indicates an Activity Stream-enhanced RSS feed competes with the very well established RSS icon. Hence it is not an easy task to propose such an icon. No reason not to try it anyway:
If you do not spot it at once I failed. But here is a hint: Look for 16x16 pixels bottom right.
Each icon is a visual abstraction of a concept or idea. The idea behind my waves are an electroencephalogram (EEG) or seismograph, that tracks several sensors. Each for a special aspect of the observed body. You can also see it as a river, where the user from the shoreline can scoop out some information of interest.
Why green? Green is bio and bio is life. And green is not orange.
To the extent possible under law, Matthias Müller-Prove has waived all copyright and related or neighboring rights to Icons for Activity Streams. Hamburg, 8-Oct-2009.
|16x16||42x42 with 1 pixel transparent frame|
|#3 - blue is also not orange|
|#2 - draft, do not use|
The lines are based on the 'almost equal to' charachter of the font Bitstream Vera Sans. But Helvetica works as well if you move the lines a bit together. To me it is important that the left and right edges look straight cut. Many other fonts have more brush-like narrow ends.