Use of symbol # in vba code

The type-declaration character for Double is the number sign (#). Also called HASH
Other type declaration characters are:

1. Integer %
2. Long &
3. Currency @
4. Single !
5. Double #
6. String $

Don't understand the significance of # here.

It implies that when the expression is evaluated, the number in front of the type declaration character is treated as a specific data type instead of as a Variant.
See this example, which are basically the same.

Sub Sample1()
    Dim a#

    a = 1.2

    Debug.Print a
End Sub

Sub Sample2()
    Dim a As Double

    a = 1.2

    Debug.Print a
End Sub

EDIT
Let me explain it a little more in detail.
Consider this two procedures

Sub Sample1()
    Dim a As Double, b As Integer

    b = 32767
    a = b * 100

    Debug.Print a
End Sub

Sub Sample2()
    Dim a As Double, b As Integer

    b = 32767
    a = b * 100#

    Debug.Print a
End Sub

Question: One of them will fail. Can you guess which one?
Ans: The 1st procedure Sub Sample1() will fail.
Reason:
In Sample2, when you do b * 100# the result of calculation will be of type Double. Since it is within the limits of Double, so the calculation succeeds and the result is assigned to variable a.
Now in Sample1, when you do b * 100 the result of calculation will be of type Integer, since both the operands are of type integer. But the result of calculation exceeds the limits of Integer storage. As a result it will error out.