Download the logo by right-clicking (secondary-clicking) the image above and selecting "Save As..." or similar option.
If you've been linked to this, you probably made a language mistake and whoever sent this to you cared enough to point it out. The best thing to do is read the details and see where you went wrong.
"Anniversary" comes from the Latin "annus" ("year") and "versus" (roughly: "turn"), so it only applies to years. Specifically for months, there is the related term "mensiversary", but if that is not desired, a more general term may be "commemoration" or "milestone".
Logo and details are available under the Standard Free License. Please credit this page or any of the accounts listed on my homepage.