When describing a letter (or aerogram) that Mrs. Sen receives in the mail, Lahiri alludes to Mahatma Gandhi, as seen in the following passage:
Weeks passed at Mrs. Sen’s before he found a blue aerogram, grainy to the touch, crammed with stamps showing a bald man at a spinning wheel, and blackened by postmarks. […]
For the first time she embraced [Eliot], clasping his face to her sari, surrounding him with her odor of mothballs and cumin. She seized the letter from his hands.
When Lahiri describes the “bald man at a spinning wheel” that appears on the stamps on the letter, she is alluding to Gandhi, who appeared in stamps like this for many years. Gandhi was a nonviolent activist who helped lead India to freedom from British colonial rule. One of the ways he did this was via the Swadeshi movement, which centered on Indians spinning their own textiles rather than purchasing British imports, effectively boycotting Britain in the process. The stamp shows Gandhi at his spinning wheel to symbolize his leadership in the Swadeshi movement.
It is notable that after Mrs. Sen receives this envelope bearing a proud symbol of Indian nationalism, she hugs Eliot “for the first time” and then “seize[s] the letter from his hands.” Lahiri implies here that just seeing Gandhi’s image floods Mrs. Sen with joy as he is an important symbol of her home and suggests that someone from her family back in India has written to her.