The brown, hardened, foam-like structure with horizontal ridges is characteristic of a mantis egg case. A female mantis produces a frothy material that hardens into this protective casing, which can contain dozens to hundreds of eggs.
Should you remove it?
If possible, leave it alone. Mantis nymphs are harmless to people and can be useful in the garden because they eat many insects.
If it is attached somewhere inconvenient, you can carefully relocate the entire egg case to a sheltered branch or similar outdoor surface rather than scraping it apart.
One caution: identification from a photo isn’t 100% certain, because some other insects also produce egg masses that look somewhat similar. But the structure shown is highly consistent with a mantis ootheca.
