At Amazon, level is public. Microsoft, only the title (Senior etc) is visible not the precise level is visible is my impression. At Google, it can be public but apparently can also be hidden. At Facebook it's always hidden.

I'm interviewing engineers right now, it is tough to judge what their current level mapping is especially if they come from Facebook. You can guesstimate from their resume accomplishments and tenure but the rest is just interview performance or asking directly - there are staff engineers that get there from 3 years out of college and there are seniors that are at that level for a decade.