Step 1: Identify the sentence type.
The indirect sentence is an imperative (order) - not to permit. Converting to direct speech requires an imperative command form.
Step 2: Apply the conversion rule.
Negative indirect imperatives become Do not + base verb in direct speech. The reporting clause becomes said to the Guard.
Step 3: Confirm option 1.
Do not permit vehicles inside the restricted area is the correct imperative form. Options 2, 3, and 4 use wrong or non-standard structures.
\[ \boxed{\text{Do not permit vehicles inside the restricted area}} \]