And in New York's biggest arenas, that vaccination card will be their ticket back to indoor events.
This week, Madison Square Garden and Barclays Center will be the first major indoor sports venues to allow fans who show proof of full vaccination to purchase tickets to NBA and NHL games, albeit with limited seating and a mask mandate.
Ben Diamond, a Knicks and Rangers fan who started the blog Concrete New York, that has chronicled the city's sports fans' thoughts and experiences during the pandemic, told ABC News that he and other fans were relieved when the arena announced the plan.
"I'd personally feel better going to the Garden if I was fully vaccinated, and knew that others had their shots," said Diamond, 25, who received his first vaccine shot last week.
Public health experts and business experts predict that more indoor businesses will ask for vaccination confirmations from customers as more locations begin reopening. However, they warned that such a program would not immediately bring their businesses back to pre-pandemic times, as millions of Americans are still waiting for their shots and thousands of new COVID-19 cases are still recorded daily.
Dr. Dean Winslow, an infectious disease physician at Stanford Health Care, told ABC News that MSG and Barclays Center's strategy is effective since it doesn't rely heavily on vaccination rates to safely allow fans inside.
The arenas are only at 10% capacity, and any ticket buyer that is not 14 days out of their second shot will have to present a negative coronavirus test, according to MSG's website. All fans must also adhere to the mask mandate, regardless of their vaccination status.
"I do think people do have to understand that any time you have to gather indoors, outside of your immediate family, you are assuming a risk, but the risk [at MSG] is manageable," Winslow told ABC News.
Winslow said other sports locations will likely be instituting similar policies during the spring and summer if they want to welcome their fans back safely -- but it may take time.
"Right now, with such a small percentage vaccinated, it's going to be a few months before you see these policies adopted on a widespread basis," he predicted.
Lauren Bock Mullins, an assistant professor of management at the College of Staten Island, told ABC News the policy will likely go beyond sporting events.
Indoor businesses that have been most impacted by the pandemic, such as movie theaters, concert halls, shops and restaurants, have been yearning to get their customers back without spreading the virus, she said.
In many cities and towns, those businesses have reopened and have strict health policies, including limited seating and mask mandates.
Mullins said a proof of vaccination option may be used by bigger businesses and chains first, but smaller mom-and-pops will be keeping their eyes on the plan's effectiveness.
"If they do it well, I don't see why others would not want to follow suit," Mullins told ABC News.
Public health experts warned that businesses that do impose a policy that allows for more vaccinated customers to enter a venue need to be careful.
Philip Alcabes, the director of the public health program at Hunter College, said that the country's vaccination rate is moving at a good pace nationally, but there are still some counties that are lagging behind, particularly in lower-income and minority neighborhoods.
Proof of vaccination policies, at this point, would accentuate the vaccine inequality on an economic level, Alcabes said.
"These sorts of systems that require people to show proof of something always invite opportunities to have inequities," Alcabes told ABC News.
The professor added that there is still the threat of rising cases from the COVID-19 variants, and people need to stick to social distancing, even if they already received their shots, until more people are vaccinated.
Alcabes said if indoor businesses do start implementing the proof of vaccination policy, people who have been hesitant to get the vaccine may do so, if only to begin resuming their normal lives.
Diamond said he has heard from a lot of sports fans in the New York area who are more than willing to get their shots and return to their pre-pandemic activities.
He said fans feel a sense of appreciation and acknowledgment when they see rewards being offered to those getting vaccinated.
"Some fans will say, 'OK I don't want to miss out on this,'" Diamond said. "They feel they've done a good job being safe."