Yes, Beatrix, that is what you think it is.
"Is that what I think it is?" is a good (and often overused) line because it suggests so much. Whatever object/thing is about to be revealed, it's something with enough renown that the character speaking already has an idea of what it is. But it's also so intense/badass/rare that the character remains hesitant to name it outright.
Is that what I think it is? Yep, it totally is.
This supercut from Supercutonline pulls together 41 famous (and not-so-famous) uses of the shopworn line, and it's enjoyable not only to attempt to identify the film in question but to try to remember what the thing in question was, and if it was in fact what they thought it was. A full list of the source films is in the YouTube description.