Some time ago, the Smalltalk community tried to define a 'Powered by Smalltalk' logo. None of the suggested logos became a de-facto standard.
As part of the Smalltalk Central initiative, the Smalltalk Industry Council now advocates for the use of [|] (bracket, vertical bar, bracket), as in: '[|] Powered by Smalltalk'. [|] represents a unique aspect of Smalltalk syntax, it's easy to include in both graphic and text based content, and, over time, will become a recognized logo.
The individual look of the logo should be tailored to the web site. Notice how the one on Smalltalk Central blends nicely into the view. And being a simple text string, it can easily be added to your email sig file.
For Smalltalk advocacy sites that are not Smalltalk based, consider using '[|] Powering Smalltalk' (I've added a simple one to the Toronto Smalltalk User Group web site) and please link it to www.Smalltalk-Central.com ... let's make it the 1st Googled Smalltalk site.
[|] was created by Joseph Pelrine, in addition to the not-so-secret 'Knights of the Square Bracket'. It has an honourable history, and the community can make it relevant. I invite you all to join in using [|] to symbolize Smalltalk.