I too recently had the pleasure of a genuine 'We are glad for your Service' by a US Customs guy at the Airport. - And I was not in Uniform - (admittedly a NATO visa in passport).. On arrival in the UK, the customs guy at Gatwick appeared to smile, but I cannot confirm this.
...Have also had a free breakfast whilst in a US eatery after a night shift - courtesy of an 'anonymous' client unknown to me..
...Clearly, the uniform does it in the US. - but we all know that.