As far as I know, nothing whatsoever to do with the US State, but according to an article on our Intranet today (i.e. lifted directly, including the logo):

17th May marks International Day against Homophobia and Transphobia (IDAHO). Campaigns and initiatives take place around the world to combat prejudice against LGBT people.

IDAHO was founded in 2005 and 17th May is chosen because it marks the anniversary of the day in 1990 when the World Health Organisation removed homosexuality from it's list of mental diseases.

(Snipped out info relating to a local event our LGBT Staff Network will be attending)

More information is available on www.idahomophobia.org