I often teach a lesson which brings up this issue - the short answer is, yes you should smile much more than you usually do when in Russia.

I like to smile at people if I don't know them and our eye meet. Smiles are infectious and its good to spread joy, however small.

I have heard that we Americans smile a lot...I didn't know if I agreed, so, I paid attention to this for the past couple of months, and yes we use our smiles as a main nonverbal communication: as a greeting, an agreement, a welcome, a passing hello, an approval, an encouragement...the list could go on and on!! When smiled at, if you do not smile back, you communicate a negative message. Interesting question!!