Do they have same meaning? Is there any difference by intuition?
- What does it signify?
- What does this signify?
Both it and this are pronouns that refer to other objects or concepts. As used in these sentences, they each refer to something that has been identified in a prior sentence.
While both are nominally singular, it is slightly more aggressively so, and would be used when a discrete single thing or concept has been previously identified.
They raised the blue flag. What does it signify?
The sentence could either mean
What does the blue flag signify
What does the raising of the blue flag signify.
To convey either of these meanings, you could also say
What does this signify?.
This is a somewhat broader term and can be used to refer to a single concept or to multiple things that together form a pattern or concept.
They ran around, fired cannons and shouted Hurrah! What does this signify?
The collection of events is being discussed as a whole, and this refers to that amalgam. In this case, it would generally seem too narrow.
You could say
They ran around, fired cannons and shouted "Hurrah"! That was a strange set of behaviors. What does it signify?
In this example, the events have been summarized into a discrete item, set and it becomes appropriate. But this could also be used.
In many cases, either would do. In some, this would be preferred.
There's a subtle difference.
"This" is indicative. For example, if you pointed at something, you would refer to it as "this".
"It" is referential. If you mentioned something, you would refer to it as "it".
So, "What does it signify" asks what the thing you are talking about signifies (usually the subject of a recent phrase). Similarly, "What does this signify?" asks what the thing you indicated (drew attention to) signifies.
Here's an example where the two refer to different things.
"That book is Jeff's favorite. What does this signify?"
This asks what Jeff's fondness for the book signifies. Jeff's fondness for the book is the thing you just indicated.
"That book is Jeff's favorite. What does it signify?"
This asks what the book itself signifies. The book is the subject of the preceding phrase.
("It" need not always refer to the subject of the previous phrase, of course, that's just how it works in this case. Consider, "Mary saw the beautiful bicycle in the store window. She wanted it." This is not saying she wants herself!)
"You remember the book that is Jeff's favorite? What does it signify?"
The preceding sentence doesn't really indicate anything. You cannot change "it" to "this" here.
They appear to mean the same thing, but again it depends on how they're used. For example "this" refers to an object.
That book belongs to George, but this book belongs to me.
That book is with George, but it belongs to me.