c. 1913 AK1E60
Black probably wool maillot pantaloon. Also called a maillot tank pantaloon. A.k.a. maillot pantaloon tank, tank maillot pantaloon, and so on, but often just maillot pantaloon.
L. Bare arms.
Kellerman stands for a postcard pinup in a risqué one piece bare-legged bathing suit (1). Most "good girls" wouldn't wear this at all. Kellerman wears it to the beach and in the movies. The full postcard with the label (2).
Kellerman is not so much the "bad girl" but the advocate of women's rights. And these include the right to swim in a bathing costume that is efficient and safe. It is hard to estimate the date of this postcard but we know that the core idea of the bare-legged bathing suit is aggressively advanced by Kellerman from as early as her Revere Beach arrest in 1907 (AK0750) to her introduction of the maillot to the movies in Neptune's Daughter (AK1410).
"Miss Annette Kellerman, Champion Lady Swimmer and Diver of the World, Sears, Melbourne, [Australia]," postcard, collected wikimedia.org. Date is estimated and could be anywhere from the late oughts to the late teens. 2 pictures.