The “XSI flower” was a graphic design element used with releases 4.0 and 5.0.

I call it the “flower” because I found it in a folder named “XSI_FLOWER”. It appears to have been done in Photoshop (there was a .PSD file there) and this JPG:

UPDATES:
Thanks to Hirazi Blue (in the comments) and takita (XSI list) for pointing out that the flower logo was created by me company using Softimage|XSI itself.

In the comments, Hirazi also mentions that:

There was a nice 5 page article specifically about this design in the August 2007, #93 issue of 3D World (pages 44-48).

So, I dug up (aka googled) some more info:

• The cover page for the XSI 4.0 New Features document includes this:
  

  Cover: “Water Flowers” designed for Softimage Co. by Me Company, using SOFTIMAGE|XSI.

• On xsibase I found this quote from Gareth Morgan (Senior Product Manager, Softimage):
  

  “We’re really proud of the new symbol. Yes, of course – it was 100% designed and realized in XSI. The amazing designers at Me Company (London, UK)worked with our Creative Director and designed the ‘Water Flower’ exclusively for v.4.0 – it’s a strong, colourful symbol that is easily identifiable, translates from print to screen beautifully, and communicates the vision of our brand for XSI. Me Company designed the Water Flower as model in XSI, and used the lighting and texturing tools in to give the flower it’s look and feel, and then used the advanced rendering capabilities in XSI to output the design.”

• The “water flower” logo was mentioned in the book More than a Name: An Introduction to Branding:
  
• Some info about Me Company:
  

  Although the majority of Me Company’s output is in two dimensions, the production process involves three, “XSI is our illustration tool of choice,” says Paul. “It’s the way we express our ideas.” The results, which Paul calls ‘hi-res stills’, capture the world of possibilities Paul and his creative allies envision in response to a particular brief. What makes this work is a faith in the value of the creative process itself: “We follow a line that interests us and try hard to push things forward.”