Because you can

"On 20 Nov 2007 three teenage monks were brutally beaten by police. One of the monks, Tsering Gyaltsen, was beaten particularly severely after police found him wearing a photo of the Dalai Lama around his neck. China is a State Party to the UN Convention against Torture and the UN Convention on the Rights of the Child. In both these conventions, torture has been absolutely prohibited under any circumstances but in reality it occurs unabated in Tibet with impunity.

In Tibet, it is commonplace for Tibetans to be detained, arrested, imprisoned and tortured for exercising their right to freedom of expression and opinion, and other rights intrinsic to the freedom of thought and religion. Security forces routinely resort to arbitrary arrest, imprisonment, and torture in response to non-violent protests, including displaying the Tibetan flag or any other innocuous symbols of cultural identity, staging peaceful demonstrations, possessing photographs of the Dalai Lama, and pasting and distributing political leaflets."--from the Human Rights Situation in Tibet Annual Report 2007 by the Tibetan Centre for Human Rights and Democracy

Because in Tibet it could cost them their lives, where anywhere else it costs us nothing, fly the flag. Carry a picture of the Dalai Lama, stick it to your cubicle wall, to a notebook, to your car window. Not because you are Buddhist, or Tibetan, but because you are human. And because you have rights as a human that your government will acknowledge and protect. That cross that's hanging around your neck? Touch it. Be grateful. And fly the flag for a Free Tibet.