As noted by French site Consomac [Google Translate], iGuide Media filed a priority trademark for an icon that appears to correspond to a HomeKit "Home" app on March 12, 2015 in Jamaica, and has now filed again in the United States on September 14. The trademark applies to a long list of electronics and home products, including thermostats, smoke detectors, window shades, garage door openers, and more.
iGuide Media is a shell company that has filed trademarks on Apple's behalf in the past, ahead of the 2010 launch of the original iPad.
The icon is depicted in the trademark application as an H with a roof on it to form a house, with the icon placed on an orange background. It is similar in color to the HomeKit icons on Apple's own website, but the design is decidedly different.
Apple's release plans for a HomeKit app are unclear. It is not known if the company intends to launch a HomeKit app for public use in the future, or if the icon in today's trademark filing corresponds to a dedicated app. It could also be an icon simply intended to represent HomeKit going forward, in developer documentation and on product packaging.