id  doc_id  datetime      user   event
---|------|------------|--------|--------
1  | 10   | 04/03/2018 | john   | sign
2  | 10   | 05/03/2018 | anna   | sign
3  | 10   | 11/03/2018 | paul   | reject
4  | 10   | 23/03/2018 | marc   | sign
5  | 11   | 23/03/2018 | john   | sign

user   num_of_signed_docs
-----|-------------------|
john |  1                |
anna |  0                |
paul |  0                |
marc |  1                |

select user, sum(case when event = 'sign' then 1 else 0 end) as num_signs
from audittable
group by user;

SELECT user, COUNT(event = 'sign') AS `num_of_signed_docs`
FROM audittable
WHERE `id` > (SELECT `id` FROM audittable
                WHERE `event` = 'reject'
                ORDER BY `id` DESC LIMIT 1)
GROUP BY user;

select t.username, sum(t.type) num_of_signed_docs from (
select a.username,
case
  when event = 'reject' then 0
  when exists
  (select 1 from audit where doc_id = a.doc_id and
    datetime > a.datetime and event = 'reject')
  then 0
  else 1 end as type
from audit a
) t
group by t.username

Create Table signed
(
id Int,
doc_id Int,
dt Datetime,
usr VarChar(25),
event VarChar(25)
)
Insert Into signed Values

(1,10,'2018/03/04','john','sign'),
(2,10,'2018/03/05','anna','sign'),
(3,10,'2018/03/11','paul','reject'),
(4,10,'2018/03/23','marc','sign'),
(5,11,'2018/03/23','john','sign')

With cte1 As
(
Select id,usr From signed
), cte2 As
(
   Select id as rid,usr, count(*) As numb From signed
   Where dt >
      (
         Select Top 1 dt From signed Where event = 'reject'
      )
   Group by id,usr
)

Select min(id) As mid,cte1.usr,Max(isnull(numb,0)) As num_signed_docs
From cte1 Left Join
cte2 On cte1.usr = cte2.usr
Group by cte1.usr
Order by mid

mid usr     num_signed_docs
1   john    1
2   anna    0
3   paul    0
4   marc    1