Yellow flags and hefty fines follow safety Brandon Meriweather wherever he plays in the NFL, and now he will take aim for the Giants after the desperate team signed him off the street Sunday to add experience to a depleted secondary.  Meriweather, 31, is best known for helmet-to-helmet hits that he has put on receivers across the league since New England drafted him out of Miami in 2007, but he is also a two-time Pro Bowler. He played the last three seasons in Washington, and the Giants welcomed him into their training camp Sunday after losing four defensive backs to injury in their preseason opener against the Bengals.  FOLLOW THE DAILY NEWS SPORTS ON FACEBOOK. "LIKE" US HERE  Meriweather adds aggressiveness to a unit that was tentative in the loss to Cincinnati. He also brings unwanted attention as he has twice been suspended and fined more than $100,000.  “I’m excited, man,” Meriweather said after his first practice. “Any time you can come to a great organization, you’ve always got to be excited and ready to help.”  Little has gone right for the secondary since camp began. Rookie safeties Landon Collins (MCL sprain) and Mykkele Thompson (ruptured Achilles) went down against the Bengals. Collins is expected to return within a month, but Thompson was placed on injured reserve as he will need the year to recover.  “We’re still trying to find our guys,” said cornerback Prince Amukamara, who is recovering from a groin injury. “We just have to roll with it.”  RELATED: GIANTS SECONDARY PRIMARY CONCERN FOR COUGHLIN  The signing of Meriweather displayed just how desperate the Giants have become in attempting to replace Antrel Rolle and Stevie Brown in the secondary. Those two players were allowed to walk in free agency, and then a rash of injuries occurred in the last week. Also in Cincinnati, Jayron Hosley suffered a concussion and Chykie Brown sprained his knee. Safety Nat Berhe was already down with a calf strain and Amukamara continues to make his way back from the groin pull he suffered when opening his hip while covering wideout Victor Cruz in practice.  “It just seems like it’s always been happening to us,” Amukamara said. “The Giants are known for the ‘Next Man Up’ mentality. It’s really unfortunate for the rookies because they’re just getting their feet wet. It’s definitely tough and can hurt their confidence. I think the right type of guy can persevere through that.”  Tom Coughlin knows the depth chart and its related injury updates as well as anyone. He made sure his team knew that Friday’s performance against the Bengals was unacceptable, as well. He related to his current players that they lost the physical battle, going by his gauge of how his team performed against the run and whether they were being knocked off the ball or doing the knocking.  “I felt like on the defensive side we got punched in the mouth pretty early,” Amukamara said.  Safety Jeromy Miles, a six-year veteran, noted the need for improved tackling as well as talking.  “We just have to stick to our guns and keep developing,” Miles said. “I’ve put an onus on myself this year that I am as vocal as possible, make sure everyone can hear the specific checks from me.”  Miles will compete for a starting job while the rookies rehabilitate. He maintained “we have a long way to go,” and that the season kicks off in Dallas, against quarterback Tony Romo and wideout Dez Bryant. Meriweather is one more body on the field. Coaches and players hope he will bring a boost.  “The biggest measure will be to see how we will bounce back,” Amukamara said.  MOBILE USER? SEE THE GIANTS VIDEO HERE
The Giants’ secondary may not have gotten much better on Sunday, but it sure did get a lot nastier.