Demonstratives provide deictic [Pragmatics – 1.1.] information with respect to proximity or distalness of the noun that is referred to [Pragmatics - 5.1.3.]. They are always definite in meaning. The following example shows a proximal referent to the signer, which is indicated by the demonstrative this.
this sheet
'this sheet'
The demonstrative this above is articulated in the center of the signing space while the demonstrative that uses more peripheral space with respect to the midline of the body and it shows a distal referent to the signer.
that pen
'that pen'