I've been looking some request examples and as far as I know it's not REST, as it's not using resources in the url, only parameters.
Examples:
Create topic
http://sns.us-east-1.amazonaws.com/
?Name=My-Topic
&Action=CreateTopic
&SignatureVersion=2
&SignatureMethod=HmacSHA256
&Timestamp=2010-03-31T12%3A00%3A00.000Z
&AWSAccessKeyId=(AWS Access Key ID)
&Signature=gfzIF53exFVdpSNb8AiwN3Lv%2FNYXh6S%2Br3yySK70oX4%3
Add Permission:
http://sns.us-east-1.amazonaws.com/
?TopicArn=arn%3Aaws%3Asns%3Aus-east-1%3A123456789012%3AMy-Test
&ActionName.member.1=Publish
&ActionName.member.2=GetTopicAttributes
&Label=NewPermission
&AWSAccountId.member.1=987654321000
&AWSAccountId.member.2=876543210000
&Action=AddPermission
&SignatureVersion=2
&SignatureMethod=HmacSHA256
&Timestamp=2010-03-31T12%3A00%3A00.000Z
&AWSAccessKeyId=(AWS Access Key ID)
&Signature=k%2FAU%2FKp13pjndwJ7rr1sZszy6MZMlOhRBCHx1ZaZFiw%3D
More info: http://aws.amazon.com/en/sns/faqs/