Many 'child-safety' applications (web filters, monitoring tools etc.) use 'stealth' techniques to hide their presence. The reason they give for this is because they consider it the parents choice to let their children know if they are being monitored or not. I do not agree with this type of covert action.
Personally I believe that children (just like anyone else) should be made aware if their activity is being monitored or filtered. If you feel that your children cannot be trusted to use the Internet wisely then perhaps they should not be allowed to use it unsupervised. It is not just a matter of trust but education too. Children should be taught safe Web use and by having a visible symbol showing that their activity is being monitored they may think twice about their actions and learn why filtering is taking place. If you filter their browsing but don't tell them why then they will expect to sit down at any computer and have the same kind of invisible protection. This false sense of security is dangerous.
This is why SafeSearchLock has the visible icon in the corner and we urge parents to tell their children why it is there and how it is helping to protect them, rather than let them think it's because you don't trust them.